# unicorn/prefer-native-coercion-functions

> Require passing `String`, `Number`, `BigInt`, `Boolean` and `Symbol` directly instead of wrapping them

A function that only passes its first parameter to `String`, `Number`, `BigInt`, `Boolean` or `Symbol` does what the built-in already does. Pass the built-in itself.

The rule also reports `value => value` as the callback of `every`, `filter`, `find`, `findIndex`, `findLast`, `findLastIndex` and `some`. Those methods only check whether the result is truthy, so `Boolean` does the same thing.

{/* 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-native-coercion-functions" = "error" # or "warn"
```

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

## Examples

Reported:

{/* bad {"count": 3} */}
```js
const ids = rows.map(id => Number(id));

const names = users.map(user => user.name).filter(name => name);

function toText(value) {
  return String(value);
}
```

Not reported:

{/* good */}
```js
const ids = rows.map(Number);

const names = users.map(user => user.name).filter(Boolean);

const toText = String;
```

A function that does anything more isn't reported. Neither is a TypeScript type guard, because `Boolean` doesn't narrow the type:

{/* good */}
```ts
const prices = rows.map(row => Number(row.price));

const found = items.filter((item): item is Item => Boolean(item));
```