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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 Function.prototype.call, 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 = String.prototype.toUpperCase.call({
  toString: function toString() {
    return 'abcdef';

const b = String.prototype.toUpperCase.call(true);

// 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

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

Document Tags and Contributors

Last updated by: doubleOrt,