Suggest an edit

Improve this article

Refine the answer for “Changing length manually”. Your changes go to moderation before they’re published.

Approval required

Content

What you’re changing

Title (EN)

Short answer (EN)

Shown above the full answer for quick recall.

Answer (EN)

The `length` property of a JavaScript array is **special**.
It does not just show the length, it also **controls the number of elements**.
If you change it manually, it directly affects the array's contents.

## Example 1: Decreasing length

```javascript
const arr = [1, 2, 3, 4, 5];
arr.length = 3;

console.log(arr); // [1, 2, 3]
```

If you decrease `length`, **all elements with larger indexes are removed**.

## Example 2: Increasing length

```javascript
const arr = [1, 2, 3];
arr.length = 6;

console.log(arr);       // [1, 2, 3, <3 empty items>]
console.log(arr[4]);    // undefined
```

If you increase `length`, **"empty slots"** (empty items) are added.
They are not equal to `undefined` - they are **empty cells** that "don't exist" in a sense,
so, for example, `forEach()` skips them.

## Example 3: Clearing an array with length = 0

```javascript
const arr = [10, 20, 30];
arr.length = 0;

console.log(arr); // []
```

A very convenient way to **clear an array** - without recreating it.

## Important to know:

| Action | What happens |
|---|---|
| `arr.length = smaller` | truncates the array |
| `arr.length = larger` | adds empty cells |
| `arr.length = 0` | clears the array |
| `arr.length` read only | shows the number of elements |

## In short:

> The `length` property does not just tell you "how many elements",
> it **controls the array's size**.
> Decrease it and you remove elements, increase it and you create empty slots.

Markdown · drag & drop images · ⌘B / ⌘I shortcuts248 words

For the reviewer

Note to the moderator (optional)

Visible only to the moderator. Helps review go faster.