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® 2026 Language Specification # sec-string.prototype.touppercase |