toUpperCase() and toLowerCase()

Syntax

str.toUpperCase()
str.toLowerCase()

Examples

const text = "Hello World";

console.log(text.toUpperCase()); // "HELLO WORLD"
console.log(text.toLowerCase()); // "hello world"

function isSameWord(a, b) {
  return a.toLowerCase() === b.toLowerCase();
}

console.log(isSameWord("Hello", "hello")); // true
console.log(isSameWord("JavaScript", "javascript")); // true

// Also useful for case-insensitive search
const items = ["Apple", "Banana", "Cherry"];
const search = "banana";
const found = items.find(item => item.toLowerCase() === search.toLowerCase());
console.log(found); // "Banana"

Best practices

• Convert both sides to the same case before comparing user input against known values, to make comparisons case-insensitive
• Use toLocaleUpperCase()/toLocaleLowerCase() instead when working with locale-specific characters, like Turkish "İ"/"i"
• Remember these return new strings - the original is never modified
• Store data in a consistent case (like all lowercase) if you frequently need case-insensitive lookups, rather than converting on every comparison

At a glance

Purpose

Application logic and interaction

File extension

.js · .mjs

Runs in

Browsers and JavaScript runtimes

Usually used with

HTML, CSS and Web APIs

Specifications & further reading

• ECMAScript specification

Related JavaScript documentation