# unicorn/no-useless-length-check

> Disallow checking an array's length next to `.some()` or `.every()` where it changes nothing

`some()` returns `false` for an empty array, so `items.length > 0 && items.some(...)` gives the same answer without the length check. `every()` returns `true` for an empty array, so `items.length === 0 || items.every(...)` does too.

`length !== 0` counts the same as `length > 0`. The check can come before or after the call, and both must be on the same variable.

{/* 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/no-useless-length-check" = "error" # or "warn"
```

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

## Examples

Reported:

{/* bad {"count": 3} */}
```js
if (errors.length > 0 && errors.some(error => error.fatal)) {
  stop();
}

const isDone = tasks.length === 0 || tasks.every(task => task.done);
const hasDraft = posts.some(post => post.draft) && posts.length !== 0;
```

Not reported:

{/* good */}
```js
if (errors.some(error => error.fatal)) {
  stop();
}

const isDone = tasks.every(task => task.done);
const hasDraft = posts.some(post => post.draft);
```

Here the check does change the result, because `every()` alone is `true` for an empty array:

{/* good */}
```js
const allPassed = tests.length > 0 && tests.every(test => test.passed);
```