String.prototype.toUpperCase()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The toUpperCase() method of String values returns this string converted to uppercase.

Try it

const sentence = "The quick brown fox jumps over the lazy dog.";

console.log(sentence.toUpperCase());
// Expected output: "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG."

Syntax

js
toUpperCase()

Parameters

None.

Return value

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

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

js
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:

js
const a = String.prototype.toUpperCase.call({
  toString() {
    return "abcdef";
  },
});

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

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

Specifications

Specification
ECMAScript® 2025 Language Specification
# sec-string.prototype.touppercase

Browser compatibility

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See also