String.prototype.concat()

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

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.

See also

• Array.prototype.concat()
• Assignment operators