# unicorn/prefer-spread

> Require the spread operator instead of `Array.from()`, `concat()`, `slice()` and `toSpliced()`

There are many ways to copy or join arrays: `Array.from(items)`, `items.slice()`, `items.slice(0)`, `items.toSpliced()`, `items.concat(more)`. `[...items]` replaces all of them, and shows in one place what ends up in the new array.

`--fix` rewrites all of them except `concat()`, where the rule can't tell whether an argument is an array to spread or a single item.

{/* Generated by src/codegen/lint-rule-docs.ts. Do not edit this section. */}

## Configure

Off by default. To turn it on:

```toml bunfig.toml
[lint.rules]
"unicorn/prefer-spread" = "error" # or "warn"
```

{/* End of the generated section. */}

## Examples

Reported:

{/* bad {"count": 4} */}
```js
const links = Array.from(document.querySelectorAll("a"));
const copy = items.slice();
const sorted = scores.toSpliced().sort();
const all = items.concat(more, last);
```

Not reported:

{/* good */}
```js
const links = [...document.querySelectorAll("a")];
const copy = [...items];
const sorted = [...scores].sort();
const all = [...items, ...more, last];
```

Calls that do more than copy aren't reported. Neither is `slice()` on a variable named `buffer`, `arrayBuffer`, `blob` or `file`, or `concat()` on a string or on a capitalized name such as `Buffer`:

{/* good */}
```js
const squares = Array.from(numbers, n => n * n);
const empty = Array.from({ length: 3 });
const rest = items.slice(1);
const chunk = blob.slice();
const greeting = "Hello, ".concat(user.name);
const body = Buffer.concat(chunks);
```

## When not to use it

Spread needs an iterable. `Array.from()` also accepts an object that only has a `length` and indexes, so keep it for those.