content/snippets/js/s/for-in-for-of-foreach.md
---
title: What is the difference between JavaScript's for...in, for...of and forEach?
shortTitle: JavaScript iteration methods comparison
type: question
language: javascript
tags: [array,object,iterator]
cover: lake-loop
excerpt: Learn the differences between the three most commonly used iteration methods in JavaScript, that often confuse beginners and veterans alike.
listed: true
dateModified: 2021-06-12
---
`for...in` is used to iterate over all enumerable properties of an object, including inherited enumerable properties. This iteration statement can be used with arrays strings or plain objects, but not with `Map` or `Set` objects.
```js
for (let prop in ['a', 'b', 'c'])
console.log(prop); // 0, 1, 2 (array indexes)
for (let prop in 'str')
console.log(prop); // 0, 1, 2 (string indexes)
for (let prop in {a: 1, b: 2, c: 3})
console.log(prop); // a, b, c (object property names)
for (let prop in new Set(['a', 'b', 'a', 'd']))
console.log(prop); // undefined (no enumerable properties)
```
`for...of` is used to iterate over iterable objects, iterating over their values instead of their properties. This iteration statement can be used with arrays, strings, `Map` or `Set` objects, but not with plain objects.
```js
for (let val of ['a', 'b', 'c'])
console.log(val); // a, b, c (array values)
for (let val of 'str')
console.log(val); // s, t, r (string characters)
for (let val of {a: 1, b: 2, c: 3})
console.log(prop); // TypeError (not iterable)
for (let val of new Set(['a', 'b', 'a', 'd']))
console.log(val); // a, b, d (Set values)
```
Finally, `forEach()` is a method of the `Array` prototype, which allows you to iterate over the elements of an array. While `forEach()` only iterates over arrays, it can access both the value and the index of each element while iterating.
```js
['a', 'b', 'c'].forEach(
val => console.log(val) // a, b, c (array values)
);
['a', 'b', 'c'].forEach(
(val, i) => console.log(i) // 0, 1, 2 (array indexes)
);
```