JavaScript do...while Loop

The do...while loop is a control flow statement in JavaScript that executes a block of code once before checking a specified condition. It then repeats the loop as long as the condition remains true.

Syntax:

do {
  // Code to be executed at least once
} while (condition);

Condition: The expression that is evaluated after each iteration. If true, the loop continues; otherwise, it terminates.

Why it is Used:

Execution Guarantee: Ensures that the code block is executed at least once, regardless of the initial condition.

let userInput;

do {
  userInput = prompt('Enter a value (type "exit" to end):');
  console.log('You entered:', userInput);
} while (userInput !== 'exit');

User Input Validation: Useful for scenarios where you want to prompt the user for input and continue until a specific condition is met.

let isValidInput;

do {
  userInput = prompt('Enter a valid number:');
  isValidInput = !isNaN(userInput);
} while (!isValidInput);

Examples:

Basic do...while Loop:

let count = 0;

do {
  console.log(count);
  count++;
} while (count < 5);

User Input Validation:

let isValidInput;

do {
  userInput = prompt('Enter a valid number:');
  isValidInput = !isNaN(userInput);
} while (!isValidInput);

 

Summary 

The do...while loop in JavaScript guarantees the execution of the code block at least once and then repeats the loop based on a specified condition. It is particularly useful for scenarios involving user input validation or situations where you want to ensure the code runs at least once.