forEach in an array

JavaScriptJunior~2 min read

The forEach() method in JavaScript is used to iterate over array elements and perform an action on each element. Unlike map() and filter(), it returns nothing - it is used only for side effects (logging, a request, modifying data, and so on).

Syntax

javascript

array.forEach((element, index, array) => {
  // action on the element
});

Callback parameters:

Argument	Description
`element`	The current array element
`index`	The index of the current element
`array`	The original array itself

Example 1. Logging elements to the console

javascript

const numbers = [1, 2, 3];

numbers.forEach(num => {
  console.log(num);
});
// Outputs:
// 1
// 2
// 3

The method simply runs through each element, returning nothing.

Example 2. Modifying external data

javascript

const users = ['Tim', 'Alex', 'John'];
const greetings = [];

users.forEach(name => {
  greetings.push(`Hello, ${name}!`);
});

console.log(greetings);
// ['Hello, Tim!', 'Hello, Alex!', 'Hello, John!']

Here forEach is used to fill a new array manually (unlike map, which does this automatically).

Example 3. Working with indices

javascript

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

fruits.forEach((fruit, index) => {
  console.log(`${index + 1}. ${fruit}`);
});
// 1. apple
// 2. banana
// 3. cherry

Common mistakes and limitations

Does not return a new array

javascript

const result = [1, 2, 3].forEach(n => n * 2);
console.log(result); // undefined

Use map() if you need to get a new array. 2. You cannot break the loop (break or return)

javascript

[1, 2, 3].forEach(num => {
  if (num === 2) return; // will not stop the loop
  console.log(num);
});
// Outputs: 1, 3

If you need to break the loop, use a regular for or for...of. 3. Does not work with async/await as expected

javascript

await array.forEach(async item => {
  await fetch(item); // will not wait for all requests
});

For asynchronous operations it's better to use:

javascript

for (const item of array) {
  await fetch(item);
}

When to use `forEach()`

Goal	Does `forEach()` fit
Perform an action for each element	Yes
Transform the array	No - use `map()`
Filter elements	No - use `filter()`
Find an element	No - use `find()`
Break the loop	No - use `for`

Short version:

forEach() - performs an action for each element, returning nothing.

Memory formula: arr.forEach(action) -> returns nothing.

Comparison with `map()` and `filter()`

Method	Returns a new array	Mutates the original	Can be broken	Main purpose
forEach()	No	No	No	Just iterate
map()	Yes	No	No	Transform data
filter()	Yes	No	No	Filter elements

Short Answer

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