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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 |
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