String.prototype.toUpperCase()

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

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Syntax

str.toUpperCase()

Return value

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

Errors thrown

A TypeError will be thrown if you call this method on null or undefined (via Function.prototype.call, for example).

Description

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.

Examples

Basic usage

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
String.prototype.toUpperCase.call(undefined);

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

• String.prototype.toLocaleLowerCase()
• String.prototype.toLocaleUpperCase()
• String.prototype.toLowerCase()