JavaScript

This page explains the three parts of a JavaScript for loop: initialization, condition, and update.

Goal: read and write a fixed-count loop safely, while knowing what each part controls.

for loops

A for loop is useful when a block should repeat a known number of times or while a counter moves through a range.

for (let i = 0; i < 5; i += 1) {
  console.log(`Iteration ${i + 1}`);
}

Initialization

let i = 0 runs once before the first check.

Condition

i < 5 is checked before each iteration. When it becomes false, the loop ends.

Update

i += 1 runs after the body and moves the loop toward its end.

Process an array by index

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

for (let i = 0; i < fruits.length; i += 1) {
  console.log(fruits[i]);
}

The condition uses fruits.length, so the loop stops before the index goes past the last element.

Keep the loop safe

• Make sure the update changes the value used by the condition.
• Use break when a search can stop early, and continue when one item should be skipped.
• Use while when the number of iterations is not known in advance and the condition is the main idea.
• For arrays, for...of, filter(), or map() may express the intent more clearly than an index loop.

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