The While Loop

The while loop executes a block of code as long as a specified condition is true.

Syntax

while (condition) {  // code block to be executed}

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Example

In the following example, the code inside the loop runs repeatedly as long as the variable i is less than 5:

let i = 0;let text = "";‍while (i < 5) {  text += "The number is " + i + "<br>";  i++;}

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If you forget to increase the variable used in the condition, the loop will never end and can crash your browser.

The Do While Loop

The do while loop is a variant of the while loop. It executes the code block once before checking the condition, and then repeats the loop as long as the condition is true.

Syntax

do {  // code block to be executed} while (condition);

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Example

In the example below, the loop will execute at least once, even if the initial condition is false, because the code block is executed before the condition is tested:

let i = 0;let text = "";‍do {  text += "The number is " + i + "<br>";  i++;} while (i < 5);

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Remember to increase the variable used in the condition, or the loop will never end!

Comparing For and While

A while loop is similar to a for loop but without the initialization and increment expressions.

Example Using For Loop

This loop uses a for loop to collect the car names from the cars array:

const cars = ["BMW", "Audi", "Tesla"];let text = "";‍for (let i = 0; i < cars.length; i++) {  text += cars[i] + " ";}

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Example Using While Loop

This loop uses a while loop to collect the car names from the cars array:

const cars = ["BMW", "Audi", "Tesla"];let i = 0;let text = "";‍
while (i < cars.length) 
{  
text += cars[i] + " ";  i++;

}‍

Both loops achieve the same result but use different looping structures.

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