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

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

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
concatChrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes

Legend

Full support  
Full support

See also

Last modified:

, by MDN contributors
Related Topics
  1. Standard built-in objects
  2. String
  3. Properties
    1. String.prototype
    2. String.prototype.length
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    3. String.prototype.anchor()
    4. String.prototype.big()
    5. String.prototype.blink()
    6. String.prototype.bold()
    7. String.prototype.charAt()
    8. String.prototype.charCodeAt()
    9. String.prototype.codePointAt()
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    11. String.prototype.endsWith()
    12. String.prototype.fixed()
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    15. String.prototype.includes()
    16. String.prototype.indexOf()
    17. String.prototype.italics()
    18. String.prototype.lastIndexOf()
    19. String.prototype.link()
    20. String.prototype.localeCompare()
    21. String.prototype.match()
    22. String.prototype.matchAll()
    23. String.prototype.normalize()
    24. String.prototype.padEnd()
    25. String.prototype.padStart()
    26. String.prototype.quote()
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    28. String.prototype.replace()
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    32. String.prototype.split()
    33. String.prototype.startsWith()
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    35. String.prototype.sub()
    36. String.prototype.substr()
    37. String.prototype.substring()
    38. String.prototype.sup()
    39. String.prototype.toLocaleLowerCase()
    40. String.prototype.toLocaleUpperCase()
    41. String.prototype.toLowerCase()
    42. String.prototype.toSource()
    43. String.prototype.toString()
    44. String.prototype.toUpperCase()
    45. String.prototype.trim()
    46. String.prototype.trimEnd()
    47. String.prototype.trimStart()
    48. String.prototype.valueOf()
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  5. Inheritance:
  6. Function
  7. Properties
    1. Function.arguments
    2. Function.arity
    3. Function.caller
    4. Function.displayName
    5. Function.length
    6. Function.name
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