JavaScript: loops

Loops repeat a block of code while a condition holds or while items remain in a collection.

What you will learn

How for, while, and for...of differ
How to traverse an array without an off-by-one error
How break and continue change a loop

Minimal examples

const colors = ['red', 'green', 'blue'];
for (const color of colors) {
  console.log(color);
}

for (let i = 0; i < 3; i++) {
  console.log(i);
}

Use for...of when you need each value. Use a counted for loop when the index or a precise number of iterations matters.

Common mistakes

Ensure the loop condition eventually becomes false; otherwise the loop never ends.
Use i < array.length rather than i <= array.length for zero-based indexes.
Do not use for...in as the default way to read array values; it iterates property names.