Web/JavaScript/Reference/Global objects/String/repeat

The repeat() method constructs and returns a new string which contains the specified number of copies of the string on which it was called, concatenated together.

Syntax

str.repeat(count)

Parameters

count: An integer between 0 and +Infinity, indicating the number of times to repeat the string.

Return value

A new string containing the specified number of copies of the given string.

Exceptions

RangeError: repeat count must be non-negative.
RangeError: repeat count must be less than infinity and not overflow maximum string size.

Examples

Using repeat()

'abc'.repeat(-1)    // RangeError
'abc'.repeat(0)     // ''
'abc'.repeat(1)     // 'abc'
'abc'.repeat(2)     // 'abcabc'
'abc'.repeat(3.5)   // 'abcabcabc' (count will be converted to integer)
'abc'.repeat(1/0)   // RangeError

({ toString: () => 'abc', repeat: String.prototype.repeat }).repeat(2) 
// 'abcabc' (repeat() is a generic method)

Polyfill

This method has been added to the ECMAScript 2015 specification and may not be available in all JavaScript implementations yet. However, you can polyfill String.prototype.repeat() with the following snippet:

if (!String.prototype.repeat) {
  String.prototype.repeat = function(count) {
    'use strict';
    if (this == null)
      throw new TypeError('can\'t convert ' + this + ' to object');

    var str = '' + this;
    // To convert string to integer.
    count = +count;
    // Check NaN
    if (count != count)
      count = 0;

    if (count < 0)
      throw new RangeError('repeat count must be non-negative');

    if (count == Infinity)
      throw new RangeError('repeat count must be less than infinity');

    count = Math.floor(count);
    if (str.length == 0 || count == 0)
      return '';

    // Ensuring count is a 31-bit integer allows us to heavily optimize the
    // main part. But anyway, most current (August 2014) browsers can't handle
    // strings 1 << 28 chars or longer, so:
    if (str.length * count >= 1 << 28)
      throw new RangeError('repeat count must not overflow maximum string size');

    var maxCount = str.length * count;
    count = Math.floor(Math.log(count) / Math.log(2));
    while (count) {
       str += str;
       count--;
    }
    str += str.substring(0, maxCount - str.length);
    return str;
  }
}

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'String.prototype.repeat' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`repeat`	Chrome Full support 41	Edge Full support 12	Firefox Full support 24	IE No support No	Opera Full support 28	Safari Full support 9	WebView Android No support No	Chrome Android Full support 36	Firefox Android Full support 24	Opera Android Full support 28	Safari iOS Full support 9	Samsung Internet Android Full support 3.0	nodejs Full support 4.0.0 Full support 4.0.0 Full support 0.12 Disabled' Disabled' From version 0.12: this feature is behind the `--harmony` runtime flag.

Legend

Full support: Full support
No support: No support
User must explicitly enable this feature.': User must explicitly enable this feature.