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 +∞: [0, +∞), indicating the number of times to repeat the string in the newly-created string that is to be returned.

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

'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 6 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;
    count = +count;
    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 rpt = '';
    for (;;) {
      if ((count & 1) == 1) {
        rpt += str;
      }
      count >>>= 1;
      if (count == 0) {
        break;
      }
      str += str;
    }
    // Could we try:
    // return Array(count + 1).join(this);
    return rpt;
  }
}

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'String.prototype.repeat' in that specification.
Standard Initial definition.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'String.prototype.repeat' in that specification.
Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 41  24 (24) No support No support 9
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support 36 24.0 (24) No support No support No support

Document Tags and Contributors

 Last updated by: eduardoboucas,