**do...while** guarantees the loop body runs at least once because the condition is checked **after** the body executes. This is perfect for menus, prompts, and retry logic where you must act before checking the result.
1Understanding do...while Loop
do...while guarantees the loop body runs at least once because the condition is checked after the body executes. This is perfect for menus, prompts, and retry logic where you must act before checking the result.
do...while is rare in modern JavaScript because most frameworks handle UI loops. But it's perfect for retry logic and validation.
// Retry logic: try at least once
let attempts = 0;
let success = false;
do {
attempts++;
success = Math.random() > 0.7; // 30% fail rate
console.log(`Attempt ${attempts}: ${success ? 'OK' : 'fail'}`);
} while (!success && attempts < 5);
console.log(`Done in ${attempts} attempt(s)`);2Practical Example
Here is a real-world application of do...while Loop showing how it is used in production JavaScript code.
// Validate input (runs at least once)
let input;
do {
input = prompt('Enter a number > 0: ');
} while (isNaN(input) || Number(input) <= 0);
console.log('Valid input:', input);3Best Practices
Follow these guidelines when working with do...while Loop:
1. Use when the body must run at least once
2. Common for input validation loops
3. Ensure the condition will eventually be false
Tip: do...while is rare in modern JavaScript because most frameworks handle UI loops. But it's perfect for retry logic and validation.
// Retry logic: try at least once
let attempts = 0;
let success = false;
do {
attempts++;
success = Math.random() > 0.7; // 30% fail rate
console.log(`Attempt ${attempts}: ${success ? 'OK' : 'fail'}`);
} while (!success && attempts < 5);
console.log(`Done in ${attempts} attempt(s)`);