The toUpperCase() method returns the calling string value converted to uppercase (the value will be converted to a string if it isn't one).



Return value

A new string representing the calling string converted to upper case.


The toUpperCase() method returns the value of the string converted to uppercase. This method does not affect the value of the string itself since JavaScript strings are immutable.

You cannot call this method on null or undefined (via, for example) , if you do, a TypeError will be thrown.



console.log('alphabet'.toUpperCase()); // 'ALPHABET'

Conversion of non-string this values to strings

This method will convert any non-string value to a string, when you set its this to a value that is not a string: ​​​​

const a ={
  toString: function toString() {
    return 'abcdef';

const b =;

// prints out 'ABCDEF TRUE'.
console.log(a, b);

Calling on undefined and null

// TypeError;


Specification Status Comment
ECMAScript 1st Edition (ECMA-262) Standard Initial definition. Implemented in JavaScript 1.0.
ECMAScript 5.1 (ECMA-262)
The definition of 'String.prototype.toUpperCase' in that specification.
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'String.prototype.toUpperCase' in that specification.
ECMAScript Latest Draft (ECMA-262)
The definition of 'String.prototype.toUpperCase' in that specification.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
Basic supportChrome Full support YesEdge Full support YesFirefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes


Full support  
Full support

See also

Document Tags and Contributors

Last updated by: wbamberg,