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JavaScript | String.prototype.toLocaleLowerCase() Method

  • Last Updated : 02 Apr, 2020

The String.prototype.toLocaleLowerCase() method in JavaScript is a Standard built in object which returns the calling string value converted to lowercase letter on the basis of host’s current locale.


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str.toLocaleLowerCase([locale, locale, ...])


  • locale: It is optional parameter and it indicates the locale to be used to convert to lower case according to any locale-specific case mappings.

Returns Value: This method returns a string of lowercase letter.

Exceptions: This method gives two kinds of error, which are as follows:

  • RangeError: If the locale argument isn’t a valid language tag.
  • TypeError: If an array element isn’t of type string.

Below examples illustrate the String.prototype.toLocaleLowerCase() method in JavaScript:

Example 1:

const gfg = 'GeeKsForGeekS';
console.log('EN-US: ' + gfg.toLocaleLowerCase('en-US'));
console.log('TR: ' + gfg.toLocaleLowerCase('tr'));
const gfg1 = new String("String.prototype.toLocaleLowerCase()");
console.log('Result: ' + gfg1.toLocaleLowerCase());


"EN-US: geeksforgeeks"
"TR: geeksforgeeks"
"Result: string.prototype.tolocalelowercase()"

Example 2:

console.log('\u0130'.toLocaleLowerCase('tr') === 'i');  
console.log('\u0130'.toLocaleLowerCase('en-US') === 'i');
let geeks = ['tr', 'TR', 'tr-TR', 'tr-u-co-search', 'tr-x-turkish'];
console.log('\u0130'.toLocaleLowerCase(geeks) === 'i'); 



Supported Browsers: The browsers supported by String.prototype.toLocaleLowerCase() method are listed below:

  • Google Chrome
  • Firefox
  • IE
  • Opera
  • Safari
  • Edge

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