Learn JS
Array
// array
let selectedColors = ["Red","Blue"];
console.log(selectedColors);
// indexing array element.
console.log(selectedColors[0]);
output:
[ 'Red', 'Blue' ]
Red
JavaScript provides eight different data types which are
undefined,
null,
boolean,
string,
symbol,
bigint,
number, and
object.
Primitive Data type
// These are primitive data type
let name = "HelpMe" // string Literal
let age = 30; //number Literal
let isApproved = true; // boolean
let fName = undefined;
let lastname = null;
Reference Data type
// // Reference data type
// object ---->its a real life like name, address, property and more
// Array
// Function
When u concatenate Undefined with number
console.log(undefined + 10);
output: NaN
NaN - Not a Number.
When u concatenate Undefined with String
console.log(undefined + "10");
output: undefined10
While Loop
let num = 1; // initialization
while(num <=10){ // condition
console.log(num);
num++; // update step
}
output:
1
2
3
4
5
6
7
8
9
10
For Loop
for(let num=1; num <=5; num++){
console.log(num);
}
output:
1
2
3
4
5
Array
let arr = ["life",1,"22",['1',"Kiran"], 34];
console.log(arr);
output:
[ 'life', 1, '22', [ '1', 'Kiran' ], 34 ]
let arr = ["system",1,"22",['1',"Kiran"],34];
console.log(arr[0]);
output: system
let arr = ["system",1,"22",['1',"Die hard"],34];
console.log(arr[3][1]);
output: Die hard
Print Array using for loop
let arr = ["system",1,"22",['1',"Die hard"],34];
for(let i = 0; i<=arr.length; i++){
console.log(arr[i]);
}
output:
system
1
22
[ '1', 'Die hard' ]
34
undefined
Questions:
We have an array of 0's and 1's. Our task is to put all the zeroes at the start of the array
and all the 1's at the end of the array.
input: [1,0,1,1,0,0,0]
output: [0,0,0,0,1,1,1]
and all the 1's at the end of the array.
input: [1,0,1,1,0,0,0]
output: [0,0,0,0,1,1,1]
Solution:
let arr = [1,0,1,1,0,0,0];
let count0 = 0;
let count1 = 0;
for(let i = 0; i < arr.length; i++){
if(arr[i] == 0){
count0++;
}
else{
count1++;
}
}
console.log(count0, count1);
for(let i =0; i < arr.length; i++){
if(count0 > 0){
arr[i] = 0;
count0 --;
}
else{
arr[i] = 1;
}
}
console.log(arr);
output:
4 3
[
0, 0, 0, 0,
1, 1, 1
]
another solution
let arr = [1,0,1,0,0,1,0];
console.log(arr.sort());
output:
[
0, 0, 0, 0,
1, 1, 1
]
let arr = [1,0,1,0,0,1,0];
arr.sort();
console.log(arr);
output:
[
0, 0, 0, 0,
1, 1, 1
]
another solution
let arr = [0, 1, 0, 1, 1, 0];
let left = 0;
let right = arr.length -1;
while(left <= right){
if(arr[left] == 0){
left++;
}
else{
// swap
let temp = arr[left];
arr[left] = arr[right];
arr[right] = temp;
right--;
}
}
console.log(arr);
output:
[ 0, 0, 0, 1, 1, 1 ]
Let's create a program to 1,1 1,2 1,3 and 2,1 2,2 2,3 and 3,1 3,2 3,3.
skip 1,1 2,2 3,3.
skip 1,1 2,2 3,3.
continue jam statement
let n =3;
for(let i=1; i<=n; i++){
console.log(i);
for(let j =1; j<=n; j++){
if(i ==j){
continue; // continue is a jam statement
}
console.log(i,j);
}
console.log("=========================")
}
OUTPUT:
1
1 2
1 3
=========================
2
2 1
2 3
=========================
3
3 1
3 2
=========================
Another jam statement 'break'
let n =3;
for(let i=1; i<=n; i++){
console.log(i);
for(let j =1; j<=n; j++){
if(i ==j){
break;
}
console.log(i,j);
}
console.log("=========================")
}
OUTPUT:
1
=========================
2
2 1
=========================
3
3 1
3 2
=========================
Ternary Operator have 3 operands.
let mark = 50;
let result = mark >= 40 ? "pass":"fail";
console.log(result);
OUTPUT: pass
let rain = false;
let goOutside = rain == true? "don't go outside":"go outside";
console.log(goOutside);
OUTPUT: go outside
let mark = 70;
let result = mark >= 40? mark >=70 ? "Excellent": "pass":"fail";
console.log(result);
OUTPUT: Excellent
let raining = false;
let umbrella = true;
let goOut = raining == true? umbrella == true? "Go outSide": "Stay at home":"go out";
console.log(goOut);
OUTPUT: go out
Switch Case
// switch case
let weekDayNum = 5;
let weekDay;
switch(true){
case(weekDayNum ==1):
weekDay = "Monday";
break;
case(weekDayNum ==2):
weekDay = "Tuesday";
break;
case(weekDayNum ==3):
weekDay = "Wednessday";
break;
case(weekDayNum ==4):
weekDay = "Thursday";
break;
case(weekDayNum ==5):
weekDay = "Friday";
break;
case(weekDayNum ==6):
weekDay = "Satureday";
break;
case(weekDayNum ==7):
weekDay = "Sunday";
break;
// default:
// weekDay = "Any Day";
}
console.log(weekDay)
OUTPUT: Friday
Switch case is same to if-else statement.
Questions:
Create a program to find if the number is positive, negative or
zero.
let num = -2;
switch(true){
case(num > 0):
console.log("Positive");
break;
case(num < 0):
console.log("Negative");
break;
default:
console.log("Zero");
}
OUTPUT: Negative
print like below star
*
* *
* * *
* * * *
* * * * *
Solution
let n =5;
for(let row = 1; row <= n; row++){
// console.log(row);
let star = "";
for(let starCount =1; starCount <= row; starCount++){
star = star + " * ";
}
console.log(star)
}
OUTPUT:
*
* *
* * *
* * * *
* * * * *
Armstrong number
let numOriginal = 371;
let num = numOriginal;
let numDigits =0;
while( num > 0){
let lastDigit = num%10;
numDigits++;
num = parseInt(num/10);
}
console.log(numDigits)
let sum = 0;
num = numOriginal
while( num > 0){
let lastDigit = num%10;
sum = sum + Math.pow(lastDigit, numDigits);
num = parseInt(num/10);
}
console.log(sum);
let result = sum == numOriginal? "armstrong Number" : "not an armstrong Number";
console.log(result);
Print a program like below
*
**
***
****
let n = 4;
let pattern = "";
for(let row = 1; row <=n; row++){
// console.log(row);
// print space
for(let space =1; space <= n-row; space++){
pattern = pattern + " ";
}
// print star
for(let star =1; star <= row; star++){
pattern = pattern + "*";
}
pattern = pattern + '\n';
}
console.log(pattern);
output:
*
**
***
****
Print a program like below
*
* *
* * *
* * * *
let n = 4;
let pattern = "";
for(let row = 1; row <=n; row++){
// console.log(row);
// print space
for(let space =1; space <= n-row; space++){
pattern = pattern + " ";
}
// print star
for(let star =1; star <= row; star++){
pattern = pattern + " * ";
}
pattern = pattern + '\n';
}
console.log(pattern);
output:
*
* *
* * *
* * * *
Print a program like below
*
* *
* * *
* * * *
let n = 4;
let pattern = "";
for(let row = 1; row <=n; row++){
for(let star =1; star <= row; star++){
pattern = pattern + " * ";
}
pattern = pattern + '\n';
}
console.log(pattern);
Output:
*
* *
* * *
* * * *
Print a program like below
*
* *
* * *
* * * *
* * *
* *
*
let n = 4;
let pattern = "";
for(let row = 1; row <=n; row++){
console.log(row);
for(let star =1; star <= row; star++){
pattern = pattern + "* ";
}
pattern = pattern + '\n';
}
// second half trinagle
for(let row = n-1; row >= 1; row--){
console.log(row);
// print stars
for(let star = 1; star <= row; star++){
pattern = pattern + "* ";
}
pattern = pattern + '\n';
}
console.log(pattern);
output:
*
* *
* * *
* * * *
* * *
* *
*
7 MARCH TOPICS
console.log("Hi");
setTimeout(function(){
console.log("click the button");
}, 1000);
console.log("Welcome to loop")
OUTPUT:
Hi
Welcome to loop
click the button