What are loops in javascript | Types of loops in javascript

Loops in JavaScript are programming constructs that allow you to repeat a set of instructions or a block of code multiple times. 

Loops are useful for repetitive tasks and processing data efficiently. Think of loops as a way to tell your computer to do something repeatedly until a certain condition is met.

Here are some of most commonly used loops in javascript programming.

1. For loop:

This loop is used when you know in advance how many times you want to execute a block of code. Consider following syntax/example for better understanding which prints 1 to 4 numbers in console using for loop.

In following example, As soon as value of variable "i" is 5 the loop condition becomes false and loop breaks.

for (let i = 0; i < 5; i++) {
  console.log(i);
}

Output :

0
1
2
3
4

2. While loop :

This is used when you want to execute a block of code as long as a condition is true. Consider following syntax/example for better understanding which prints 1 to 3 number in console using while loop.

In following example, As soon as count variable value becomes 4 the while condition will became false and loop breaks.

let count = 0;
while (count < 4) {
    console.log(count);
    count++;
}

Output :

0
1
2
3

3. Do-While Loop :

This is similar to a while loop but ensures that the block of code is executed at least once, even if the condition is initially false.

Consider following syntax/example for better understanding. where 1 to 5 numbers are printed in console in reverse direction using do-while loop.

When num value become 1 the code inside do block is executed and after printing number 1 into console the loop breaks.

let num = 5;
do {
    console.log(num);
    num--;
while (num > 0);

Output :

5
4
3
2
1

4. For-In Loop :

This loop is used to iterate over the properties of an object. Consider following syntax/example for better understanding.

As per following example person object have 3 properties name, age and gender and the for-in loop will print each property key and value in console one by one.

const person = {
    name: "John",
    age: 25,
    gender: "Male"
};

for (let key in person) {
    console.log(key + ": " + person[key]);
}

Output :

name: John
age: 25
gender: Male

5. For-Of Loop :

This is used to iterate over the values of iterable objects like arrays, strings, or maps. Consider following syntax/example for better understanding.

As per following example the colors array have 3 values and the for-of loop will print each array element in console one by one.

const colors = ["red", "green", "blue"];

for (let color of colors) {
    console.log(color);
}

Output :

red
green
blue

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