The concat() method concatenates the string arguments to the calling string and returns a new string.

Syntax

str.concat(string2[, string3, ..., stringN])

Parameters

string2...stringN
Strings to concatenate to this string.

Return value

A new string containing the combined text of the strings provided.

Description

The concat() function concatenates the string arguments to the calling string and returns a new string. Changes to the original string or the returned string don't affect the other. If the arguments are not of the type string, they are converted to string values before concatenating.

Examples

Using concat()

The following example combines strings into a new string.

var hello = 'Hello, ';
console.log(hello.concat('Kevin', '. Have a nice day.'));
/* Hello, Kevin. Have a nice day. */

var greetList = ['Hello', ' ', 'Venkat', '!'];
"".concat(...greetList); // "Hello Venkat!"

"".concat({}); // [object Object]
"".concat([]); // ""
"".concat(null); // "null"
"".concat(true); // "true"
"".concat(4, 5); // "45"

Performance

It is strongly recommended that the assignment operators (+, +=) are used instead of the concat() method. 
According to this performance test, the assignment operators are several times faster.

Specifications

Specification Status Comment
ECMAScript 3rd Edition (ECMA-262) Standard Initial definition. Implemented in JavaScript 1.2.
ECMAScript 5.1 (ECMA-262)
The definition of 'String.prototype.concat' in that specification.
Standard  
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'String.prototype.concat' in that specification.
Standard  
ECMAScript Latest Draft (ECMA-262)
The definition of 'String.prototype.concat' in that specification.
Draft  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support Yes Yes1 Yes Yes Yes
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support Yes Yes Yes4 Yes Yes Yes

See also