# unicorn/explicit-length-check

> Require `length` and `size` to be compared with a number

`if (items.length)` relies on `0` being falsy. `if (items.length > 0)` says what you're testing. It also keeps a number out of places where you want a boolean. `items.length && render(items)` evaluates to `0` for an empty list, not `false`.

The rule also settles on one spelling for each check: `=== 0` for empty and `> 0` for not empty. It reports other ways to write them, such as `< 1`, `>= 1` and `!== 0`.

`--fix` rewrites the check wherever only its truthiness matters. In `const first = items.length && items[0]` the value itself is used, so that's reported but not fixed.

{/* 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/explicit-length-check" = "error" # or "warn"
```

Every option, set to its default:

```toml bunfig.toml
[lint.rules]
"unicorn/explicit-length-check" = ["error", {
  non-zero = "greater-than",
}]
```

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

## Examples

Reported:

{/* bad {"count": 4} */}
```js
if (items.length) {
  render(items);
}

if (!selected.size) {
  disable(button);
}

const hasErrors = errors.length >= 1;
const first = items.length && items[0];
```

Not reported:

{/* good */}
```js
if (items.length > 0) {
  render(items);
}

if (selected.size === 0) {
  disable(button);
}

const hasErrors = errors.length > 0;
const first = items.length > 0 && items[0];
```

Optional chains, `this.length` and a fallback to a number are left alone:

{/* good */}
```js
if (items?.length) {
  render(items);
}

class Queue extends Array {
  isEmpty() {
    return !this.length;
  }
}

const columns = headers.length || 1;
```

## Options

| Option | Default | What it does |
| --- | --- | --- |
| `non-zero` | `"greater-than"` | How to write "not empty": `"greater-than"` requires `> 0`, `"not-equal"` requires `!== 0`. |

{/* good {"options": [{"non-zero": "not-equal"}]} */}
```js
if (items.length !== 0) {
  render(items);
}
```

{/* bad {"options": [{"non-zero": "not-equal"}]} */}
```js
if (items.length > 0) {
  render(items);
}
```