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.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
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.
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;
}
}
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)
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'String.prototype.repeat' in that specification. |
Browser compatibility
The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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
|
Legend
- Full support
- Full support
- No support
- No support
- User must explicitly enable this feature.
- User must explicitly enable this feature.