Mastering Loops in JavaScript: A Comprehensive Guide

Why Loops Matter

Loops let you repeat a block of code without duplicating it, which is essential for working with arrays, objects, and repetitive tasks.

Overview of Loop Types

• for loop — ideal when the number of iterations is known in advance.
• while loop — repeats while a condition remains true, checked before each pass.
• do...while loop — guarantees the body runs at least once before checking the condition.
• for...in loop — iterates over the enumerable keys of an object.
• for...of loop — iterates over the values of an iterable like an array, string, or Map.

let obj = { a: 1, b: 2 };
for (let key in obj) {
    console.log(key, obj[key]);
}

let arr = [1, 2, 3];
for (let val of arr) {
    console.log(val);
}

Choosing the Right Loop

Use for...of for array values, for...in for object keys, and classic for/while loops when you need full control over the iteration logic.