Loops

Learn how to repeat a block of JavaScript code multiple times using loops.

What is a Loop?

A loop is used when we need to execute the same block of code repeatedly.

Instead of writing the same statements many times, we can use a loop and control how many times the code should execute.

Common JavaScript loop structures and their execution flow.

Common JavaScript Loops

for

for Loop

Commonly used when the number of iterations is known or controlled with a counter.

while

while Loop

Repeats code while a specified condition remains true.

do...while Loop

Executes the loop body first and checks the condition afterward.

for Loop Syntax

for (initialization; condition; update) {
    // code to execute
}

How a Loop Works

Start → Check Condition → Execute → Update → Repeat

Start Initialize counter

→

Condition true or false

→

Execute Code Run loop body

→

Update Change counter

↺ Check the condition again until it becomes false

Example 1: for Loop

Here, the loop starts from 1 and runs until the counter reaches 5.

for (let i = 1; i <= 5; i++) {
    console.log("Number:", i);
}

Output

Number: 1
Number: 2
Number: 3
Number: 4
Number: 5

Example 2: while Loop

A while loop checks its condition before each iteration. The loop continues while the condition is true.

let count = 1;

while (count <= 5) {
    console.log("Count:", count);
    count++;
}

Output

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5

Important Note

Avoid Infinite Loops

Make sure the loop condition can eventually become false.

In a counter-based loop, update the counter correctly so that the loop can stop.

Summary

Loops are used to repeat code efficiently. The main JavaScript loops are for, while, and do...while. A for loop is useful for controlled repetition, a while loop checks its condition before each iteration, and a do...while loop checks the condition after executing the loop body.