JavaScript from freeCodeCamp
1.
Understanding Uninitialized Variables
When JavaScript variables are declared, they have an initial value of undefined. If you do a mathematical operation on an undefined variable your result will be NaN which means "Not a Number". If you concatenate a string with an undefined variable, you will get a literal string of undefined.
2.
Explore Differences Between the var and let Keywords
One of the biggest problems with declaring variables with the var keyword is that you can easily overwrite variable declarations:
var camper = "James";
var camper = "David";
console.log(camper);
In the code above, the camper variable is originally declared as James, and is then overridden to be David. The console then displays the string David.
In a small application, you might not run into this type of problem. But as your codebase becomes larger, you might accidentally overwrite a variable that you did not intend to. Because this behavior does not throw an error, searching for and fixing bugs becomes more difficult.
A keyword called let was introduced in ES6, a major update to JavaScript, to solve this potential issue with the var keyword. You'll learn about other ES6 features in later challenges.
If you replace var with let in the code above, it results in an error:
let camper = "James";
let camper = "David";
The error can be seen in your browser console.
So unlike var, when you use let, a variable with the same name can only be declared once.
3.
Declare a Read-Only Variable with the const Keyword
The keyword let is not the only new way to declare variables. In ES6, you can also declare variables using the const keyword.
const has all the awesome features that let has, with the added bonus that variables declared using const are read-only. They are a constant value, which means that once a variable is assigned with const, it cannot be reassigned:
const FAV_PET = "Cats";
FAV_PET = "Dogs";
The console will display an error due to reassigning the value of FAV_PET.
You should always name variables you don't want to reassign using the const keyword. This helps when you accidentally attempt to reassign a variable that is meant to stay constant.
Note: It is common for developers to use uppercase variable identifiers for immutable values and lowercase or camelCase for mutable values (objects and arrays). You will learn more about objects, arrays, and immutable and mutable values in later challenges. Also in later challenges, you will see examples of uppercase, lowercase, or camelCase variable identifiers.
Change the code so that all variables are declared using let or const. Use let when you want the variable to change, and const when you want the variable to remain constant. Also, rename variables declared with const to conform to common practices.
4.
Compound Assignment With Augmented Division.
-=
+=
*=
/=
5.
Escaping Literal Quotes in Strings
When you are defining a string you must start and end with a single
or double quote. What happens when you need a literal quote: " or ' inside of your string?
In JavaScript, you can escape a quote from considering it as an end of string quote by placing a backslash (\) in front of the quote.
const sampleStr = "Alan said, \"Peter is learning JavaScript\".";
This signals to JavaScript that the following quote is not the end of the string, but should instead appear inside the string. So if you were to print this to the console, you would get:
Alan said, "Peter is learning JavaScript".
Use backslashes to assign a string to the myStr variable so that if you were to print it to the console, you would see:
I am a "double quoted" string inside "double quotes".
Note:
The backslash \ should not be confused with the forward slash /. They do not do the same thing.
6.
Quoting Strings with Single Quotes
String values in JavaScript may be written with single or double quotes, as long as you start and end with the same type of quote. Unlike some other programming languages, single and double quotes work the same in JavaScript.
const doubleQuoteStr = "This is a string";
const singleQuoteStr = 'This is also a string';
The reason why you might want to use one type of quote over the other
is if you want to use both in a string. This might happen if you want
to save a conversation in a string and have the conversation in quotes.
Another use for it would be saving an <a> tag with various attributes in quotes, all within a string.
const conversation = 'Finn exclaims to Jake, "Algebraic!"';
However, this becomes a problem if you need to use the outermost quotes within it. Remember, a string has the same kind of quote at the beginning and end. But if you have that same quote somewhere in the middle, the string will stop early and throw an error.
const goodStr = 'Jake asks Finn, "Hey, let\'s go on an adventure?"';
const badStr = 'Finn responds, "Let's go!"';
Here badStr will throw an error.
In the goodStr above, you can use both quotes safely by using the backslash \ as an escape character.
Note: The backslash \ should not be confused with the forward slash /. They do not do the same thing.
Solution:
const myStr = '<a href="http://www.example.com" target="_blank">Link</a>';
7.
Escape Sequences in Strings
Quotes are not the only characters that can be escaped inside a string. There are two reasons to use escaping characters:
- To allow you to use characters you may not otherwise be able to type out, such as a carriage return.
- To allow you to represent multiple quotes in a string without JavaScript misinterpreting what you mean.
| Code | Output |
|---|---|
\' | single quote |
\" | double quote |
\\ | backslash |
\n | newline |
\r | carriage return |
\t | tab |
\b | word boundary |
\f | form feed |
output should be
FirstLine
\SecondLine
ThirdLine
8.
Concatenating Strings with Plus Operator
In JavaScript, when the + operator is used with a String value, it is called the concatenation operator. You can build a new string out of other strings by concatenating them together.
Example
'My name is Alan,' + ' I concatenate.'
Note: Watch out for spaces. Concatenation does not add spaces between concatenated strings, so you'll need to add them yourself.
9.
Appending Variables to Strings
Just as we can build a string over multiple lines out of string literals, we can also append variables to a string using the plus equals (+=) operator.
Example:
const anAdjective = "awesome!";
let ourStr = "freeCodeCamp is ";
ourStr += anAdjective;
ourStr would have the value freeCodeCamp is awesome!.
10.
Find the Length of a String
You can find the length of a String value by writing .length after the string variable or string literal.
console.log("Alan Peter".length);
The value 10 would be displayed in the console.
11.
Understand String Immutability
In JavaScript, String values are immutable, which means that they cannot be altered once created.
For example, the following code:
let myStr = "Bob";
myStr[0] = "J";
cannot change the value of myStr to Job, because the contents of myStr cannot be altered. Note that this does not mean that myStr cannot be changed, just that the individual characters of a string literal cannot be changed. The only way to change myStr would be to assign it with a new string, like this:
let myStr = "Bob";
myStr = "Job";
12.
Use Bracket Notation to Find the Last Character in a String
In order to get the last letter of a string, you can subtract one from the string's length.
For example, if const firstName = "Ada", you can get the value of the last letter of the string by using firstName[firstName.length - 1].
Example:
const firstName = "Ada";
const lastLetter = firstName[firstName.length - 1];
lastLetter would have a value of the string a.
13.
Use Bracket Notation to Find the Nth-to-Last Character in a String
You can use the same principle we just used to retrieve the last character in a string to retrieve the Nth-to-last character.
For example, you can get the value of the third-to-last letter of the const firstName = "Augusta" string by using firstName[firstName.length - 3]
Example:
const firstName = "Augusta";
const thirdToLastLetter = firstName[firstName.length - 3];
thirdToLastLetter would have a value of the string s.
14.
Word Blanks
We will now use our knowledge of strings to build a "Mad Libs" style word game we're calling "Word Blanks". You will create an (optionally humorous) "Fill in the Blanks" style sentence.
In a "Mad Libs" game, you are provided sentences with some missing words, like nouns, verbs, adjectives and adverbs. You then fill in the missing pieces with words of your choice in a way that the completed sentence makes sense.
Consider this sentence - It was really ____, and we ____ ourselves ____. This sentence has three missing pieces- an adjective, a verb and an adverb, and we can add words of our choice to complete it. We can then assign the completed sentence to a variable as follows:
const sentence = "It was really " + "hot" + ", and we " + "laughed" + " ourselves " + "silly" + ".";
In this challenge, we provide you with a noun, a verb, an adjective and an adverb. You need to form a complete sentence using words of your choice, along with the words we provide.
You will need to use the string concatenation operator + to build a new string, using the provided variables: myNoun, myAdjective, myVerb, and myAdverb. You will then assign the formed string to the wordBlanks variable. You should not change the words assigned to the variables.
You will also need to account for spaces in your string, so that the final sentence has spaces between all the words. The result should be a complete sentence.
15.
Nest one Array within Another Array
You can also nest arrays within other arrays, like below:
const teams = [["Bulls", 23], ["White Sox", 45]];
This is also called a multi-dimensional array.
16.
Access Array Data with Indexes
We can access the data inside arrays using indexes.
Array indexes are written in the same bracket notation that strings
use, except that instead of specifying a character, they are specifying
an entry in the array. Like strings, arrays use zero-based indexing, so the first element in an array has an index of 0.
Example
const array = [50, 60, 70];
array[0];
const data = array[1];
array[0] is now 50, and data has the value 60.
17.
Modify Array Data With Indexes
Unlike strings, the entries of arrays are mutable and can be changed freely, even if the array was declared with const.
Example
const ourArray = [50, 40, 30];
ourArray[0] = 15;
ourArray now has the value [15, 40, 30].
18.
Access Multi-Dimensional Arrays With Indexes
One way to think of a multi-dimensional array, is as an array of arrays. When you use brackets to access your array, the first set of brackets refers to the entries in the outer-most (the first level) array, and each additional pair of brackets refers to the next level of entries inside.
Example
const arr = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9],
[[10, 11, 12], 13, 14]
];
arr[3];
arr[3][0];
arr[3][0][1];
arr[3] is [[10, 11, 12], 13, 14], arr[3][0] is [10, 11, 12], and arr[3][0][1] is 11.
myData should equal to 8.
Multidimensional array another example.
19.
Manipulate Arrays With push()
An easy way to append data to the end of an array is via the push() function.
.push() takes one or more parameters and "pushes" them onto the end of the array.
Examples:
const arr1 = [1, 2, 3];
arr1.push(4);
const arr2 = ["Stimpson", "J", "cat"];
arr2.push(["happy", "joy"]);
arr1 now has the value [1, 2, 3, 4] and arr2 has the value ["Stimpson", "J", "cat", ["happy", "joy"]].
Push ["dog", 3] onto the end of the myArray variable.
20.
Manipulate Arrays With shift()
pop() always removes the last element of an array. What if you want to remove the first?
That's where .shift() comes in. It works just like .pop(), except it removes the first element instead of the last.
Example:
const ourArray = ["Stimpson", "J", ["cat"]];
const removedFromOurArray = ourArray.shift();
removedFromOurArray would have a value of the string Stimpson, and ourArray would have ["J", ["cat"]].
Use the .shift() function to remove the first item from myArray and assign the "shifted off" value to a new variable, removedFromMyArray.
21.
Manipulate Arrays With shift()
pop() always removes the last element of an array.
What if you want to remove the first?
That's where .shift() comes in.
It works just like .pop(), except it removes the first element
instead of the last.
Example:
const ourArray = ["Stimpson", "J", ["cat"]];
const removedFromOurArray = ourArray.shift();
removedFromOurArray would have a value of the string Stimpson,
and ourArray would have ["J", ["cat"]].
Use the .shift() function to remove the first item from myArray
and assign the
"shifted off" value to a new variable, removedFromMyArray.
22.
Manipulate Arrays With pop()
Another way to change the data in an array is with the .pop() function.
.pop() is used to pop a value off of the end of an
array. We can store this popped off value by assigning it to a variable.
In other words, .pop() removes the last element from an array and returns that element.
Any type of entry can be popped off of an array - numbers, strings, even nested arrays.
const threeArr = [1, 4, 6];
const oneDown = threeArr.pop();
console.log(oneDown);
console.log(threeArr);
The first console.log will display the value 6, and the second will display the value [1, 4].
Use the .pop() function to remove the last item from myArray and assign the popped off value to a new variable, removedFromMyArray.
const myArray = [["John", 23], ["cat", 2]];
Manipulate Arrays With unshift()
Not only can you shift elements off of the beginning of an array, you can also unshift elements to the beginning of an array i.e. add elements in front of the array.
.unshift() works exactly like .push(), but instead of adding the element at the end of the array, unshift() adds the element at the beginning of the array.
Example:
const ourArray = ["Stimpson", "J", "cat"];
ourArray.shift();
ourArray.unshift("Happy");
After the shift, ourArray would have the value ["J", "cat"]. After the unshift, ourArray would have the value ["Happy", "J", "cat"].
Add ["Paul", 35] to the beginning of the myArray variable using unshift().
24.
Shopping List
Create a shopping list in the variable myList. The list should be a multi-dimensional array containing several sub-arrays.
The first element in each sub-array should contain a string with the name of the item. The second element should be a number representing the quantity i.e.
["Chocolate Bar", 15]
There should be at least 5 sub-arrays in the list.
25.
Passing Values to Functions with Arguments
Parameters are variables that act as placeholders for the values that are to be input to a function when it is called. When a function is defined, it is typically defined along with one or more parameters. The actual values that are input (or "passed") into a function when it is called are known as arguments.
Here is a function with two parameters, param1 and param2:
function testFun(param1, param2) {
console.log(param1, param2);
}
Then we can call testFun like this: testFun("Hello", "World");. We have passed two string arguments, Hello and World. Inside the function, param1 will equal the string Hello and param2 will equal the string World. Note that you could call testFun again with different arguments and the parameters would take on the value of the new arguments.
- Create a function called
functionWithArgsthat accepts two arguments and outputs their sum to the dev console. - Call the function with two numbers as arguments.
26.
Return a Value from a Function with Return
We can pass values into a function with arguments. You can use a return statement to send a value back out of a function.
Example
function plusThree(num) {
return num + 3;
}
const answer = plusThree(5);
answer has the value 8.
plusThree takes an argument for num and returns a value equal to num + 3.
27.
Global Scope and Functions
In JavaScript, scope refers to the visibility of variables. Variables which are defined outside of a function block have Global scope. This means, they can be seen everywhere in your JavaScript code.
Variables which are declared without the let or const keywords are automatically created in the global
scope. This can create unintended consequences elsewhere in your code
or when running a function again. You should always declare your
variables with let or const.
Using let or const, declare a global variable named myGlobal outside of any function. Initialize it with a value of 10.
fun1, assign 5 to oopsGlobal without using the let or const keywords
28.
Local Scope and Functions
Variables which are declared within a function, as well as the function parameters, have local scope. That means they are only visible within that function.
Here is a function myTest with a local variable called loc.
function myTest() {
const loc = "foo";
console.log(loc);
}
myTest();
console.log(loc);
The myTest() function call will display the string foo in the console. The console.log(loc) line (outside of the myTest function) will throw an error, as loc is not defined outside of the function.
29.
Global vs. Local Scope in Functions
It is possible to have both local and global variables with the same name. When you do this, the local variable takes precedence over the global variable.
In this example:
const someVar = "Hat";
function myFun() {
const someVar = "Head";
return someVar;
}
The function myFun will return the string Head because the local version of the variable is present.
Add a local variable to myOutfit function to override the value of outerWear with the string sweater.
30.
Understanding Undefined Value returned from a Function
A function can include the return statement but it does not have to. In the case that the function doesn't have a return statement, when you call it, the function processes the inner code but the returned value is undefined.
Example
let sum = 0;
function addSum(num) {
sum = sum + num;
}
addSum(3);
addSum is a function without a return statement. The function will change the global sum variable but the returned value of the function is undefined.
31.
Assignment with a Returned Value
If you'll recall from our discussion of Storing Values with the Assignment Operator, everything to the right of the equal sign is resolved before the value is assigned. This means we can take the return value of a function and assign it to a variable.
Assume we have pre-defined a function sum which adds two numbers together, then:
ourSum = sum(5, 12);
will call the sum function, which returns a value of 17 and assigns it to the ourSum variable.
Call the processArg function with an argument of 7 and assign its return value to the variable processed.
32.
Stand in Line
In Computer Science a queue is an abstract Data Structure where items are kept in order. New items can be added at the back of the queue and old items are taken off from the front of the queue.
Write a function nextInLine which takes an array (arr) and a number (item) as arguments.
Add the number to the end of the array, then remove the first element of the array.
The nextInLine function should then return the element that was removed.
33.
Understanding Boolean Values
Another data type is the Boolean. Booleans may only be one of two values: true or false. They are basically little on-off switches, where true is on and false is off. These two states are mutually exclusive.
Note: Boolean values are never written with quotes. The strings "true" and "false" are not Boolean and have no special meaning in JavaScript.
Modify the welcomeToBooleans function so that it returns true instead of false when the run button is clicked.
34.
Use Conditional Logic with If Statements
if statements are used to make decisions in code. The keyword if
tells JavaScript to execute the code in the curly braces under certain
conditions, defined in the parentheses. These conditions are known as Boolean conditions and they may only be true or false.
When the condition evaluates to true, the program executes the statement inside the curly braces. When the Boolean condition evaluates to false, the statement inside the curly braces will not execute.
Pseudocode
if (condition is true) {
statement is executed
}
Example
function test (myCondition) {
if (myCondition) {
return "It was true";
}
return "It was false";
}
test(true);
test(false);
test(true) returns the string It was true, and test(false) returns the string It was false.
When test is called with a value of true, the if statement evaluates myCondition to see if it is true or not. Since it is true, the function returns It was true. When we call test with a value of false, myCondition is not true and the statement in the curly braces is not executed and the function returns It was false.
Create an if statement inside the function to return Yes, that was true if the parameter wasThatTrue is true and return No, that was false otherwise.
35.
Comparison with the Equality Operator
There are many comparison operators in JavaScript. All of these operators return a boolean true or false value.
The most basic operator is the equality operator ==. The equality operator compares two values and returns true if they're equivalent or false if they are not. Note that equality is different from assignment (=), which assigns the value on the right of the operator to a variable on the left.
function equalityTest(myVal) {
if (myVal == 10) {
return "Equal";
}
return "Not Equal";
}
If myVal is equal to 10, the equality operator returns true, so the code in the curly braces will execute, and the function will return Equal. Otherwise, the function will return Not Equal. In order for JavaScript to compare two different data types (for example, numbers and strings), it must convert one type to another. This is known as Type Coercion. Once it does, however, it can compare terms as follows:
1 == 1 // true
1 == 2 // false
1 == '1' // true
"3" == 3 // true
Add the equality operator to the indicated line so that the function will return the string Equal when val is equivalent to 12.
36.
Comparison with the Strict Equality Operator
Strict equality (===) is the counterpart to the equality operator (==).
However, unlike the equality operator, which attempts to convert both
values being compared to a common type, the strict equality operator
does not perform a type conversion.
If the values being compared have different types, they are considered unequal, and the strict equality operator will return false.
Examples
3 === 3 // true
3 === '3' // false
In the second example, 3 is a Number type and '3' is a String type.
Use the strict equality operator in the if statement so the function will return the string Equal when val is strictly equal to 7.
37.
Practice comparing different values
In the last two challenges, we learned about the equality operator (==) and the strict equality operator (===). Let's do a quick review and practice using these operators some more.
If the values being compared are not of the same type, the equality operator will perform a type conversion, and then evaluate the values. However, the strict equality operator will compare both the data type and value as-is, without converting one type to the other.
Examples
3 == '3' returns true because JavaScript performs type conversion from string to number. 3 === '3' returns false because the types are different and type conversion is not performed.
Note: In JavaScript, you can determine the type of a variable or a value with the typeof operator, as follows:
typeof 3
typeof '3'
typeof 3 returns the string number, and typeof '3' returns the string string.
The compareEquality function in the editor compares two values using the equality operator. Modify the function so that it returns the string Equal only when the values are strictly equal.
38.
Comparison with the Inequality Operator
The inequality operator (!=) is the opposite of the equality operator. It means not equal and returns false where equality would return true and vice versa. Like the equality operator, the inequality operator will convert data types of values while comparing.
Examples
1 != 2 // true
1 != "1" // false
1 != '1' // false
1 != true // false
0 != false // false
Add the inequality operator != in the if statement so that the function will return the string Not Equal when val is not equivalent to 99.
39.
Comparison with the Strict Inequality Operator
The strict inequality operator (!==) is the logical opposite of the strict equality operator. It means "Strictly Not Equal" and returns false where strict equality would return true and vice versa. The strict inequality operator will not convert data types.
Examples
3 !== 3 // false
3 !== '3' // true
4 !== 3 // true
Add the strict inequality operator to the if statement so the function will return the string Not Equal when val is not strictly equal to 17
40.
Comparison with the Greater Than Operator
The greater than operator (>) compares the values of two numbers. If the number to the left is greater than the number to the right, it returns true. Otherwise, it returns false.
Like the equality operator, the greater than operator will convert data types of values while comparing.
Examples
5 > 3 // true
7 > '3' // true
2 > 3 // false
'1' > 9 // false
Add the greater than operator to the indicated lines so that the return statements make sense.
41.
Comparison with the Greater Than Or Equal To Operator
The greater than or equal to operator (>=) compares the values of two numbers. If the number to the left is greater than or equal to the number to the right, it returns true. Otherwise, it returns false.
Like the equality operator, the greater than or equal to operator will convert data types while comparing.
Examples
6 >= 6 // true
7 >= '3' // true
2 >= 3 // false
'7' >= 9 // false
Add the greater than or equal to operator to the indicated lines so that the return statements make sense.
42.
Comparison with the Less Than Operator
The less than operator (<) compares the values of two numbers. If the number to the left is less than the number to the right, it returns true. Otherwise, it returns false. Like the equality operator, the less than operator converts data types while comparing.
Examples
2 < 5 // true
'3' < 7 // true
5 < 5 // false
3 < 2 // false
'8' < 4 // false
Add the less than operator to the indicated lines so that the return statements make sense.
43.
Comparison with the Less Than Or Equal To Operator
The less than or equal to operator (<=) compares the values of two numbers. If the number to the left is less than or equal to the number to the right, it returns true. If the number on the left is greater than the number on the right, it returns false. Like the equality operator, the less than or equal to operator converts data types.
Examples
4 <= 5 // true
'7' <= 7 // true
5 <= 5 // true
3 <= 2 // false
'8' <= 4 // false
Add the less than or equal to operator to the indicated lines so that the return statements make sense.
44.
Comparisons with the Logical And Operator
Sometimes you will need to test more than one thing at a time. The logical and operator (&&) returns true if and only if the operands to the left and right of it are true.
The same effect could be achieved by nesting an if statement inside another if:
if (num > 5) {
if (num < 10) {
return "Yes";
}
}
return "No";
will only return Yes if num is greater than 5 and less than 10. The same logic can be written as:
if (num > 5 && num < 10) {
return "Yes";
}
return "No";
Replace the two if statements with one statement, using the && operator, which will return the string Yes if val is less than or equal to 50 and greater than or equal to 25. Otherwise, will return the string No.
45.
Comparisons with the Logical Or Operator
The logical or operator (||) returns true if either of the operands is true. Otherwise, it returns false.
The logical or operator is composed of two pipe symbols: (||). This can typically be found between your Backspace and Enter keys.
The pattern below should look familiar from prior waypoints:
if (num > 10) {
return "No";
}
if (num < 5) {
return "No";
}
return "Yes";
will return Yes only if num is between 5 and 10 (5 and 10 included). The same logic can be written as:
if (num > 10 || num < 5) {
return "No";
}
return "Yes";
Combine the two if statements into one statement which returns the string Outside if val is not between 10 and 20, inclusive. Otherwise, return the string Inside.
46.
Introducing Else Statements
When a condition for an if statement is true, the block
of code following it is executed. What about when that condition is
false? Normally nothing would happen. With an else statement, an alternate block of code can be executed.
if (num > 10) {
return "Bigger than 10";
} else {
return "10 or Less";
}
Combine the if statements into a single if/else statement.
47.
Introducing Else If Statements
If you have multiple conditions that need to be addressed, you can chain if statements together with else if statements.
if (num > 15) {
return "Bigger than 15";
} else if (num < 5) {
return "Smaller than 5";
} else {
return "Between 5 and 15";
}
Convert the logic to use else if statements.
48.
Logical Order in If Else Statements
Order is important in if, else if statements.
The function is executed from top to bottom so you will want to be careful of what statement comes first.
Take these two functions as an example.
Here's the first:
function foo(x) {
if (x < 1) {
return "Less than one";
} else if (x < 2) {
return "Less than two";
} else {
return "Greater than or equal to two";
}
}
And the second just switches the order of the statements:
function bar(x) {
if (x < 2) {
return "Less than two";
} else if (x < 1) {
return "Less than one";
} else {
return "Greater than or equal to two";
}
}
While these two functions look nearly identical if we pass a number to both we get different outputs.
foo(0)
bar(0)
foo(0) will return the string Less than one, and bar(0) will return the string Less than two.
Change the order of logic in the function so that it will return the correct statements in all cases.
49.
Chaining If Else Statements
if/else statements can be chained together for complex logic. Here is pseudocode of multiple chained if / else if statements:
if (condition1) {
statement1
} else if (condition2) {
statement2
} else if (condition3) {
statement3
. . .
} else {
statementN
}
Write chained if/else if statements to fulfill the following conditions:
num < 5 - return Tiny
num < 10 - return Small
num < 15 - return Medium
num < 20 - return Large
num >= 20 - return Huge
50.
Golf Code
In the game of golf, each hole has a par, meaning, the average number of strokes a golfer is expected to make in order to sink the ball in the hole to complete the play. Depending on how far above or below par your strokes are, there is a different nickname.
Your function will be passed par and strokes
arguments. Return the correct string according to this table which
lists the strokes in order of priority; top (highest) to bottom
(lowest):
| Strokes | Return |
|---|---|
| 1 | "Hole-in-one!" |
| <= par - 2 | "Eagle" |
| par - 1 | "Birdie" |
| par | "Par" |
| par + 1 | "Bogey" |
| par + 2 | "Double Bogey" |
| >= par + 3 | "Go Home!" |
par and strokes will always be numeric and positive. We have added an array of all the names for your convenience.
51.
Selecting from Many Options with Switch Statements
If you have many options to choose from, use a switch statement. A switch statement tests a value and can have many case statements which define various possible values. Statements are executed from the first matched case value until a break is encountered.
Here is an example of a switch statement:
switch(lowercaseLetter) {
case "a":
console.log("A");
break;
case "b":
console.log("B");
break;
}
case values are tested with strict equality (===). The break tells JavaScript to stop executing statements. If the break is omitted, the next statement will be executed.
Write a switch statement which tests val and sets answer for the following conditions:
1 - alpha
2 - beta
3 - gamma
4 - delta
52.
Adding a Default Option in Switch Statements
In a switch statement you may not be able to specify all possible values as case statements. Instead, you can add the default statement which will be executed if no matching case statements are found. Think of it like the final else statement in an if/else chain.
A default statement should be the last case.
switch (num) {
case value1:
statement1;
break;
case value2:
statement2;
break;
...
default:
defaultStatement;
break;
}
Write a switch statement to set answer for the following conditions:
a - apple
b - bird
c - cat
default - stuff
53.
Multiple Identical Options in Switch Statements
If the break statement is omitted from a switch statement's case, the following case statement(s) are executed until a break is encountered. If you have multiple inputs with the same output, you can represent them in a switch statement like this:
let result = "";
switch(val) {
case 1:
case 2:
case 3:
result = "1, 2, or 3";
break;
case 4:
result = "4 alone";
}
Cases for 1, 2, and 3 will all produce the same result.
Write a switch statement to set answer for the following ranges:
1-3 - Low
4-6 - Mid
7-9 - High
Note: You will need to have a case statement for each number in the range.
54.
Replacing If Else Chains with Switch
If you have many options to choose from, a switch statement can be easier to write than many chained if/else if statements. The following:
if (val === 1) {
answer = "a";
} else if (val === 2) {
answer = "b";
} else {
answer = "c";
}
can be replaced with:
switch(val) {
case 1:
answer = "a";
break;
case 2:
answer = "b";
break;
default:
answer = "c";
}
Change the chained if/else if statements into a switch statement.
anyhow cmplte 113 today
55.
Returning Boolean Values from Functions
You may recall from Comparison with the Equality Operator that all comparison operators return a boolean true or false value.
Sometimes people use an if/else statement to do a comparison, like this:
function isEqual(a, b) {
if (a === b) {
return true;
} else {
return false;
}
}
But there's a better way to do this. Since === returns true or false, we can return the result of the comparison:
function isEqual(a, b) {
return a === b;
}
Fix the function isLess to remove the if/else statements.
56.
Return Early Pattern for Functions
When a return statement is reached, the execution of the current function stops and control returns to the calling location.
Example
function myFun() {
console.log("Hello");
return "World";
console.log("byebye")
}
myFun();
The above will display the string Hello in the console, and return the string World. The string byebye will never display in the console, because the function exits at the return statement.
Modify the function abTest so that if a or b are less than 0 the function will immediately exit with a value of undefined.
Hint
Remember that undefined is a keyword, not a string.
57.
Counting Cards
In the casino game Blackjack, a player can gain an advantage over the house by keeping track of the relative number of high and low cards remaining in the deck. This is called Card Counting.
Having more high cards remaining in the deck favors the player. Each card is assigned a value according to the table below. When the count is positive, the player should bet high. When the count is zero or negative, the player should bet low.
| Count Change | Cards |
|---|---|
| +1 | 2, 3, 4, 5, 6 |
| 0 | 7, 8, 9 |
| -1 | 10, 'J', 'Q', 'K', 'A' |
You will write a card counting function. It will receive a card parameter, which can be a number or a string, and increment or decrement the global count
variable according to the card's value (see table). The function will
then return a string with the current count and the string Bet if the count is positive, or Hold if the count is zero or negative. The current count and the player's decision (Bet or Hold) should be separated by a single space.
Example Outputs: -3 Hold or 5 Bet
Hint
Do NOT reset count to 0 when value is 7, 8, or 9.
Do NOT return an array.
Do NOT include quotes (single or double) in the output.
58.
Build JavaScript Objects
You may have heard the term object before.
Objects are similar to arrays, except that instead of using indexes to access and modify their data, you access the data in objects through what are called properties.
Objects are useful for storing data in a structured way, and can represent real world objects, like a cat.
Here's a sample cat object:
const cat = {
"name": "Whiskers",
"legs": 4,
"tails": 1,
"enemies": ["Water", "Dogs"]
};
In this example, all the properties are stored as strings, such as name, legs, and tails. However, you can also use numbers as properties. You can even omit the quotes for single-word string properties, as follows:
const anotherObject = {
make: "Ford",
5: "five",
"model": "focus"
};
However, if your object has any non-string properties, JavaScript will automatically typecast them as strings.
Make an object that represents a dog called myDog which contains the properties name (a string), legs, tails and friends.
You can set these object properties to whatever values you want, as long as name is a string, legs and tails are numbers, and friends is an array.
59.
Accessing Object Properties with Dot Notation
There are two ways to access the properties of an object: dot notation (.) and bracket notation ([]), similar to an array.
Dot notation is what you use when you know the name of the property you're trying to access ahead of time.
Here is a sample of using dot notation (.) to read an object's property:
const myObj = {
prop1: "val1",
prop2: "val2"
};
const prop1val = myObj.prop1;
const prop2val = myObj.prop2;
prop1val would have a value of the string val1, and prop2val would have a value of the string val2.
Read in the property values of testObj using dot notation. Set the variable hatValue equal to the object's property hat and set the variable shirtValue equal to the object's property shirt.
60.
Accessing Object Properties with Bracket Notation
The second way to access the properties of an object is bracket notation ([]). If the property of the object you are trying to access has a space in its name, you will need to use bracket notation.
However, you can still use bracket notation on object properties without spaces.
Here is a sample of using bracket notation to read an object's property:
const myObj = {
"Space Name": "Kirk",
"More Space": "Spock",
"NoSpace": "USS Enterprise"
};
myObj["Space Name"];
myObj['More Space'];
myObj["NoSpace"];
myObj["Space Name"] would be the string Kirk, myObj['More Space'] would be the string Spock, and myObj["NoSpace"] would be the string USS Enterprise.
Note that property names with spaces in them must be in quotes (single or double).
Read the values of the properties an entree and the drink of testObj using bracket notation and assign them to entreeValue and drinkValue respectively.
61.
Accessing Object Properties with Variables
Another use of bracket notation on objects is to access a property which is stored as the value of a variable. This can be very useful for iterating through an object's properties or when accessing a lookup table.
Here is an example of using a variable to access a property:
const dogs = {
Fido: "Mutt",
Hunter: "Doberman",
Snoopie: "Beagle"
};
const myDog = "Hunter";
const myBreed = dogs[myDog];
console.log(myBreed);
The string Doberman would be displayed in the console.
Another way you can use this concept is when the property's name is collected dynamically during the program execution, as follows:
const someObj = {
propName: "John"
};
function propPrefix(str) {
const s = "prop";
return s + str;
}
const someProp = propPrefix("Name");
console.log(someObj[someProp]);
someProp would have a value of the string propName, and the string John would be displayed in the console.
Note that we do not use quotes around the variable name when using it to access the property because we are using the value of the variable, not the name.
Set the playerNumber variable to 16. Then, use the variable to look up the player's name and assign it to player.
62.
Updating Object Properties
After you've created a JavaScript object, you can update its properties at any time just like you would update any other variable. You can use either dot or bracket notation to update.
For example, let's look at ourDog:
const ourDog = {
"name": "Camper",
"legs": 4,
"tails": 1,
"friends": ["everything!"]
};
Since he's a particularly happy dog, let's change his name to the string Happy Camper. Here's how we update his object's name property: ourDog.name = "Happy Camper"; or ourDog["name"] = "Happy Camper"; Now when we evaluate ourDog.name, instead of getting Camper, we'll get his new name, Happy Camper.
Update the myDog object's name property. Let's change her name from Coder to Happy Coder. You can use either dot or bracket notation.
63.
Add New Properties to a JavaScript Object
You can add new properties to existing JavaScript objects the same way you would modify them.
Here's how we would add a bark property to ourDog:
ourDog.bark = "bow-wow";
or
ourDog["bark"] = "bow-wow";
Now when we evaluate ourDog.bark, we'll get his bark, bow-wow.
Example:
const ourDog = {
"name": "Camper",
"legs": 4,
"tails": 1,
"friends": ["everything!"]
};
ourDog.bark = "bow-wow";
Add a bark property to myDog and set it to a dog sound, such as "woof". You may use either dot or bracket notation.
64.
Delete Properties from a JavaScript Object
We can also delete properties from objects like this:
delete ourDog.bark;
Example:
const ourDog = {
"name": "Camper",
"legs": 4,
"tails": 1,
"friends": ["everything!"],
"bark": "bow-wow"
};
delete ourDog.bark;
After the last line shown above, ourDog looks like:
{
"name": "Camper",
"legs": 4,
"tails": 1,
"friends": ["everything!"]
}
Delete the tails property from myDog. You may use either dot or bracket notation.
64.
Using Objects for Lookups
Objects can be thought of as a key/value storage, like a dictionary.
If you have tabular data, you can use an object to lookup values rather
than a switch statement or an if/else chain. This is most useful when you know that your input data is limited to a certain range.
Here is an example of a simple reverse alphabet lookup:
const alpha = {
1:"Z",
2:"Y",
3:"X",
4:"W",
...
24:"C",
25:"B",
26:"A"
};
alpha[2];
alpha[24];
const value = 2;
alpha[value];
alpha[2] is the string Y, alpha[24] is the string C, and alpha[value] is the string Y.
Convert the switch statement into an object called lookup. Use it to look up val and assign the associated string to the result variable.
65.
Testing Objects for Properties
Sometimes it is useful to check if the property of a given object exists or not. We can use the .hasOwnProperty(propname) method of objects to determine if that object has the given property name. .hasOwnProperty() returns true or false if the property is found or not.
Example
const myObj = {
top: "hat",
bottom: "pants"
};
myObj.hasOwnProperty("top");
myObj.hasOwnProperty("middle");
The first hasOwnProperty returns true, while the second returns false.
Modify the function checkObj to test if an object passed to the function (obj) contains a specific property (checkProp). If the property is found, return that property's value. If not, return "Not Found".
66.
Manipulating Complex Objects
Sometimes you may want to store data in a flexible Data Structure. A JavaScript object is one way to handle flexible data. They allow for arbitrary combinations of strings, numbers, booleans, arrays, functions, and objects.
Here's an example of a complex data structure:
const ourMusic = [
{
"artist": "Daft Punk",
"title": "Homework",
"release_year": 1997,
"formats": [
"CD",
"Cassette",
"LP"
],
"gold": true
}
];
This is an array which contains one object inside. The object has various pieces of metadata about an album. It also has a nested formats
array. If you want to add more album records, you can do this by adding
records to the top level array. Objects hold data in a property, which
has a key-value format. In the example above, "artist": "Daft Punk" is a property that has a key of artist and a value of Daft Punk. JavaScript Object Notation or JSON is a related data interchange format used to store data.
{
"artist": "Daft Punk",
"title": "Homework",
"release_year": 1997,
"formats": [
"CD",
"Cassette",
"LP"
],
"gold": true
}
Note: You will need to place a comma after every object in the array, unless it is the last object in the array.
Add a new album to the myMusic array. Add artist and title strings, release_year number, and a formats array of strings.
67.
Accessing Nested Objects
The sub-properties of objects can be accessed by chaining together the dot or bracket notation.
Here is a nested object:
const ourStorage = {
"desk": {
"drawer": "stapler"
},
"cabinet": {
"top drawer": {
"folder1": "a file",
"folder2": "secrets"
},
"bottom drawer": "soda"
}
};
ourStorage.cabinet["top drawer"].folder2;
ourStorage.desk.drawer;
ourStorage.cabinet["top drawer"].folder2 would be the string secrets, and ourStorage.desk.drawer would be the string stapler.
Access the myStorage object and assign the contents of the glove box property to the gloveBoxContents variable. Use dot notation for all properties where possible, otherwise use bracket notation.
67.
Accessing Nested Arrays
As we have seen in earlier examples, objects can contain both nested objects and nested arrays. Similar to accessing nested objects, array bracket notation can be chained to access nested arrays.
Here is an example of how to access a nested array:
const ourPets = [
{
animalType: "cat",
names: [
"Meowzer",
"Fluffy",
"Kit-Cat"
]
},
{
animalType: "dog",
names: [
"Spot",
"Bowser",
"Frankie"
]
}
];
ourPets[0].names[1];
ourPets[1].names[0];
ourPets[0].names[1] would be the string Fluffy, and ourPets[1].names[0] would be the string Spot.
Using dot and bracket notation, set the variable secondTree to the second item in the trees list from the myPlants object.
68.
Record Collection
You are given an object literal representing a part of your musical album collection. Each album has a unique id number as its key and several other properties. Not all albums have complete information.
You start with an updateRecords function that takes an object literal, records, containing the musical album collection, an id, a prop (like artist or tracks), and a value. Complete the function using the rules below to modify the object passed to the function.
- Your function must always return the entire record collection object.
- If
propisn'ttracksandvalueisn't an empty string, update or set that album'sproptovalue. - If
propistracksbut the album doesn't have atracksproperty, create an empty array and addvalueto it. - If
propistracksandvalueisn't an empty string, addvalueto the end of the album's existingtracksarray. - If
valueis an empty string, delete the givenpropproperty from the album.
Note: A copy of the recordCollection object is used for the tests.
69.
Iterate with JavaScript While Loops
You can run the same code multiple times by using a loop.
The first type of loop we will learn is called a while loop because it runs while a specified condition is true and stops once that condition is no longer true.
const ourArray = [];
let i = 0;
while (i < 5) {
ourArray.push(i);
i++;
}
In the code example above, the while loop will execute 5 times and append the numbers 0 through 4 to ourArray.
Let's try getting a while loop to work by pushing values to an array.
Add the numbers 5 through 0 (inclusive) in descending order to myArray using a while loop.
70.
Iterate with JavaScript For Loops
You can run the same code multiple times by using a loop.
The most common type of JavaScript loop is called a for loop because it runs for a specific number of times.
For loops are declared with three optional expressions separated by semicolons:
for (a; b; c), where a is the initialization statement, b is the condition statement, and c is the final expression.
The initialization statement is executed one time only before the loop starts. It is typically used to define and setup your loop variable.
The condition statement is evaluated at the beginning of every loop iteration and will continue as long as it evaluates to true. When the condition is false
at the start of the iteration, the loop will stop executing. This means
if the condition starts as false, your loop will never execute.
The final expression is executed at the end of each loop iteration, prior to the next condition check and is usually used to increment or decrement your loop counter.
In the following example we initialize with i = 0 and iterate while our condition i < 5 is true. We'll increment i by 1 in each loop iteration with i++ as our final expression.
const ourArray = [];
for (let i = 0; i < 5; i++) {
ourArray.push(i);
}
ourArray will now have the value [0, 1, 2, 3, 4].
Use a for loop to push the values 1 through 5 onto myArray.
70.
Iterate Odd Numbers With a For Loop
For loops don't have to iterate one at a time. By changing our final-expression, we can count by even numbers.
We'll start at i = 0 and loop while i < 10. We'll increment i by 2 each loop with i += 2.
const ourArray = [];
for (let i = 0; i < 10; i += 2) {
ourArray.push(i);
}
ourArray will now contain [0, 2, 4, 6, 8]. Let's change our initialization so we can count by odd numbers.
Push the odd numbers from 1 through 9 to myArray using a for loop.
71.
Count Backwards With a For Loop
A for loop can also count backwards, so long as we can define the right conditions.
In order to decrement by two each iteration, we'll need to change our initialization, condition, and final expression.
We'll start at i = 10 and loop while i > 0. We'll decrement i by 2 each loop with i -= 2.
const ourArray = [];
for (let i = 10; i > 0; i -= 2) {
ourArray.push(i);
}
ourArray will now contain [10, 8, 6, 4, 2].
Let's change our initialization and final expression so we can count
backwards by twos to create an array of descending odd numbers.
Push the odd numbers from 9 through 1 to myArray using a for loop.
72.
Iterate Through an Array with a For Loop
A common task in JavaScript is to iterate through the contents of an array. One way to do that is with a for loop. This code will output each element of the array arr to the console:
const arr = [10, 9, 8, 7, 6];
for (let i = 0; i < arr.length; i++) {
console.log(arr[i]);
}
Remember that arrays have zero-based indexing, which means the last index of the array is length - 1. Our condition for this loop is i < arr.length, which stops the loop when i is equal to length. In this case the last iteration is i === 4 i.e. when i becomes equal to arr.length - 1 and outputs 6 to the console. Then i increases to 5, and the loop terminates because i < arr.length is false.
Declare and initialize a variable total to 0. Use a for loop to add the value of each element of the myArr array to total.
73.
Nesting For Loops
If you have a multi-dimensional array, you can use the same logic as the prior waypoint to loop through both the array and any sub-arrays. Here is an example:
const arr = [
[1, 2], [3, 4], [5, 6]
];
for (let i = 0; i < arr.length; i++) {
for (let j = 0; j < arr[i].length; j++) {
console.log(arr[i][j]);
}
}
This outputs each sub-element in arr one at a time. Note that for the inner loop, we are checking the .length of arr[i], since arr[i] is itself an array.
Modify function multiplyAll so that it returns the product of all the numbers in the sub-arrays of arr.
74.
Iterate with JavaScript Do...While Loops
The next type of loop you will learn is called a do...while loop. It is called a do...while loop because it will first do one pass of the code inside the loop no matter what, and then continue to run the loop while the specified condition evaluates to true.
const ourArray = [];
let i = 0;
do {
ourArray.push(i);
i++;
} while (i < 5);
The example above behaves similar to other types of loops, and the resulting array will look like [0, 1, 2, 3, 4]. However, what makes the do...while
different from other loops is how it behaves when the condition fails
on the first check. Let's see this in action: Here is a regular while loop that will run the code in the loop as long as i < 5:
const ourArray = [];
let i = 5;
while (i < 5) {
ourArray.push(i);
i++;
}
In this example, we initialize the value of ourArray to an empty array and the value of i to 5. When we execute the while loop, the condition evaluates to false because i is not less than 5, so we do not execute the code inside the loop. The result is that ourArray will end up with no values added to it, and it will still look like [] when all of the code in the example above has completed running. Now, take a look at a do...while loop:
const ourArray = [];
let i = 5;
do {
ourArray.push(i);
i++;
} while (i < 5);
In this case, we initialize the value of i to 5, just like we did with the while
loop. When we get to the next line, there is no condition to evaluate,
so we go to the code inside the curly braces and execute it. We will add
a single element to the array and then increment i before we get to the condition check. When we finally evaluate the condition i < 5 on the last line, we see that i is now 6, which fails the conditional check, so we exit the loop and are done. At the end of the above example, the value of ourArray is [5]. Essentially, a do...while loop ensures that the code inside the loop will run at least once. Let's try getting a do...while loop to work by pushing values to an array.
Change the while loop in the code to a do...while loop so the loop will push only the number 10 to myArray, and i will be equal to 11 when your code has finished running.
75.
Replace Loops using Recursion
Recursion is the concept that a function can be expressed in terms of
itself. To help understand this, start by thinking about the following
task: multiply the first n elements of an array to create the product of those elements. Using a for loop, you could do this:
function multiply(arr, n) {
let product = 1;
for (let i = 0; i < n; i++) {
product *= arr[i];
}
return product;
}
However, notice that multiply(arr, n) == multiply(arr, n - 1) * arr[n - 1]. That means you can rewrite multiply in terms of itself and never need to use a loop.
function multiply(arr, n) {
if (n <= 0) {
return 1;
} else {
return multiply(arr, n - 1) * arr[n - 1];
}
}
The recursive version of multiply breaks down like this. In the base case, where n <= 0, it returns 1. For larger values of n, it calls itself, but with n - 1. That function call is evaluated in the same way, calling multiply again until n <= 0. At this point, all the functions can return and the original multiply returns the answer.
Note: Recursive functions must have a base case when they return without calling the function again (in this example, when n <= 0), otherwise they can never finish executing.
Write a recursive function, sum(arr, n), that returns the sum of the first n elements of an array arr.
76.
Profile Lookup
We have an array of objects representing different people in our contacts lists.
A lookUpProfile function that takes name and a property (prop) as arguments has been pre-written for you.
The function should check if name is an actual contact's firstName and the given property (prop) is a property of that contact.
If both are true, then return the "value" of that property.
If name does not correspond to any contacts then return the string No such contact.
If prop does not correspond to any valid properties of a contact found to match name then return the string No such property.
77.
Generate Random Fractions with JavaScript
Random numbers are useful for creating random behavior.
JavaScript has a Math.random() function that generates a random decimal number between 0 (inclusive) and 1 (exclusive). Thus Math.random() can return a 0 but never return a 1.
Note: Like Storing Values with the Assignment Operator, all function calls will be resolved before the return executes, so we can return the value of the Math.random() function.
Change randomFraction to return a random number instead of returning 0.
78.
Generate Random Whole Numbers with JavaScript
It's great that we can generate random decimal numbers, but it's even more useful if we use it to generate random whole numbers.
- Use
Math.random()to generate a random decimal. - Multiply that random decimal by
20. - Use another function,
Math.floor()to round the number down to its nearest whole number.
Remember that Math.random() can never quite return a 1 and, because we're rounding down, it's impossible to actually get 20. This technique will give us a whole number between 0 and 19.
Putting everything together, this is what our code looks like:
Math.floor(Math.random() * 20);
We are calling Math.random(), multiplying the result by 20, then passing the value to Math.floor() function to round the value down to the nearest whole number.
Use this technique to generate and return a random whole number between 0 and 9.
79.
Generate Random Whole Numbers within a Range
Instead of generating a random whole number between zero and a given number like we did before, we can generate a random whole number that falls within a range of two specific numbers.
To do this, we'll define a minimum number min and a maximum number max.
Here's the formula we'll use. Take a moment to read it and try to understand what this code is doing:
Math.floor(Math.random() * (max - min + 1)) + min
Create a function called randomRange that takes a range myMin and myMax and returns a random whole number that's greater than or equal to myMin, and is less than or equal to myMax, inclusive.
80.
Use the parseInt Function
The parseInt() function parses a string and returns an integer. Here's an example:
const a = parseInt("007");
The above function converts the string 007 to the integer 7. If the first character in the string can't be converted into a number, then it returns NaN.
Use parseInt() in the convertToInteger function so it converts the input string str into an integer, and returns it.
81.
Use the parseInt Function with a Radix
The parseInt() function parses a string and returns an
integer. It takes a second argument for the radix, which specifies the
base of the number in the string. The radix can be an integer between 2
and 36.
The function call looks like:
parseInt(string, radix);
And here's an example:
const a = parseInt("11", 2);
The radix variable says that 11 is in the binary system, or base 2. This example converts the string 11 to an integer 3.
82.
Use the Conditional (Ternary) Operator
The conditional operator, also called the ternary operator, can be used as a one line if-else expression.
The syntax is a ? b : c, where a is the condition, b is the code to run when the condition returns true, and c is the code to run when the condition returns false.
The following function uses an if/else statement to check a condition:
function findGreater(a, b) {
if(a > b) {
return "a is greater";
}
else {
return "b is greater or equal";
}
}
This can be re-written using the conditional operator:
function findGreater(a, b) {
return a > b ? "a is greater" : "b is greater or equal";
}
Use the conditional operator in the checkEqual function to check if two numbers are equal or not. The function should return either the string Equal or the string Not Equal.
83.
Use Multiple Conditional (Ternary) Operators
In the previous challenge, you used a single conditional operator. You can also chain them together to check for multiple conditions.
The following function uses if, else if, and else statements to check multiple conditions:
function findGreaterOrEqual(a, b) {
if (a === b) {
return "a and b are equal";
}
else if (a > b) {
return "a is greater";
}
else {
return "b is greater";
}
}
The above function can be re-written using multiple conditional operators:
function findGreaterOrEqual(a, b) {
return (a === b) ? "a and b are equal"
: (a > b) ? "a is greater"
: "b is greater";
}
It is considered best practice to format multiple conditional operators such that each condition is on a separate line, as shown above. Using multiple conditional operators without proper indentation may make your code hard to read. For example:
function findGreaterOrEqual(a, b) {
return (a === b) ? "a and b are equal" : (a > b) ? "a is greater" : "b is greater";
}
In the checkSign function, use multiple conditional operators - following the recommended format used in findGreaterOrEqual - to check if a number is positive, negative or zero. The function should return positive, negative or zero.
84.
Use Recursion to Create a Countdown
In a previous challenge, you learned how to use recursion to replace a for loop. Now, let's look at a more complex function that returns an array of consecutive integers starting with 1 through the number passed to the function.
As mentioned in the previous challenge, there will be a base case. The base case tells the recursive function when it no longer needs to call itself. It is a simple case where the return value is already known. There will also be a recursive call which executes the original function with different arguments. If the function is written correctly, eventually the base case will be reached.
For example, say you want to write a recursive function that returns an array containing the numbers 1 through n. This function will need to accept an argument, n, representing the final number. Then it will need to call itself with progressively smaller values of n until it reaches 1. You could write the function as follows:
function countup(n) {
if (n < 1) {
return [];
} else {
const countArray = countup(n - 1);
countArray.push(n);
return countArray;
}
}
console.log(countup(5));
The value [1, 2, 3, 4, 5] will be displayed in the console.
At first, this seems counterintuitive since the value of n decreases, but the values in the final array are increasing. This happens because the push happens last, after the recursive call has returned. At the point where n is pushed into the array, countup(n - 1) has already been evaluated and returned [1, 2, ..., n - 1].
We have defined a function called countdown with one parameter (n). The function should use recursion to return an array containing the integers n through 1 based on the n
parameter. If the function is called with a number less than 1, the
function should return an empty array. For example, calling this
function with n = 5 should return the array [5, 4, 3, 2, 1]. Your function must use recursion by calling itself and must not use loops of any kind.
85.
Use Recursion to Create a Range of Numbers
Continuing from the previous challenge, we provide you another opportunity to create a recursive function to solve a problem.
We have defined a function named rangeOfNumbers with two parameters. The function should return an array of integers which begins with a number represented by the startNum parameter and ends with a number represented by the endNum
parameter. The starting number will always be less than or equal to the
ending number. Your function must use recursion by calling itself and
not use loops of any kind. It should also work for cases where both startNum and endNum are the same.
86.