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Loops

Loops

Introduction

Loops repeat a block of code until a condition is met. JavaScript has several loop types: for, while, and do-while.

for Loop

for (initialization; condition; increment) {
  // body
}

for (let i = 0; i < 5; i++) {
  console.log(i); // 0, 1, 2, 3, 4
}

while Loop

let i = 0;
while (i < 5) {
  console.log(i); // 0, 1, 2, 3, 4
  i++;
}

do-while Loop

let i = 0;
do {
  console.log(i); // 0, 1, 2, 3, 4
  i++;
} while (i < 5);

Visual Explanation

flowchart TD
    For["for (let i=0; i&lt;5; i++)"]
    Check{"i &lt; 5?"}
    Body["console.log(i)"]
    Inc["i++"]
    End["Loop ends"]

    For --> Check
    Check -->|Yes| Body
    Body --> Inc
    Inc --> Check
    Check -->|No| End

Loop Comparison

Loop	Use Case	Condition Check
`for`	Known number of iterations	Before each iteration
`while`	Unknown iterations	Before each iteration
`do-while`	Must run at least once	After each iteration

Iterating Arrays

const fruits = ['apple', 'banana', 'orange'];

// Classic for
for (let i = 0; i < fruits.length; i++) {
  console.log(fruits[i]);
}

// for...of (ES6)
for (const fruit of fruits) {
  console.log(fruit);
}

// forEach
fruits.forEach(fruit => console.log(fruit));

Summary

for — known iteration count
while — unknown count, checked before
do-while — runs at least once
Prefer for...of for arrays (ES6)

Further Reading

MDN: Loops