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).

Syntax

toUpperCase()

Return value

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

Exceptions

TypeError
When called on null or undefined, for example, String.prototype.toUpperCase.call(undefined).

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);

Specifications

Specification
ECMAScript Language Specification (ECMAScript)
#sec-string.prototype.touppercase

Browser compatibility

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See also