String.prototype.toUpperCase()
String.prototype.toUpperCase() is a JavaScript method in the String category. Converts a string to uppercase. The syntax is str.toUpperCase(). A typical example: "Hello".toUpperCase() // "HELLO". Its time complexity is O(n), which matters when it runs over large inputs. The TypeScript signature is (): string. A close sibling is String.prototype.charAt(), which returns the character at the specified index. A close sibling is String.prototype.charCodeAt(), which returns the Unicode value of the character at the specified index. A close sibling is String.prototype.concat(), which concatenates strings together. A close sibling is String.prototype.includes(), which checks if a string contains a specified substring. More about this category: String methods for text manipulation — split, replace, trim, match, and more. Related String methods: String.prototype.charAt(), String.prototype.charCodeAt(), String.prototype.concat(), String.prototype.includes(), String.prototype.indexOf(), String.prototype.lastIndexOf(), String.prototype.match(), String.prototype.matchAll(). This page is part of the free JS Reference documentation covering 1027+ methods, each with syntax, parameters, return values, examples, and common pitfalls.