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# String.prototype.toLocaleLowerCase()

The **`toLocaleLowerCase()`** method returns the calling string
value converted to lower case, according to any locale-specific case mappings.

## Syntax

```js
toLocaleLowerCase()
toLocaleLowerCase(locales)
```

### Parameters

- `locales` _**optional**_
  - : A string with a BCP 47 language tag, or an array of such strings. Indicates the locale to be used to convert to lower case according to any locale-specific case mappings. For the general form and interpretation of the `locales` argument, see [Locale identification and negotiation](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Intl#locale_identification_and_negotiation).

### Return value

A new string representing the calling string converted to lower case, according to any
locale-specific case mappings.

### Exceptions

- A [`RangeError`](../../../globals/RangeError/RangeError.mdx) ("invalid language tag: xx_yy") is thrown if a
  `locale` argument isn't a valid language tag.
- A [`TypeError`](../../../globals/TypeError/TypeError.mdx) ("invalid element in locales argument") is thrown if an
  array element isn't of type string.

## Description

The `toLocaleLowerCase()` method returns the value of the string converted
to lower case according to any locale-specific case mappings.
`toLocaleLowerCase()` does not affect the value of the string itself. In most
cases, this will produce the same result as [`String.prototype.toLowerCase()`](../../../globals/String/prototype/toLowerCase.mdx), but for some locales, such as Turkish, whose case mappings do not
follow the default case mappings in Unicode, there may be a different result.
