String.prototype.normalize()

normalize([form])

The normalize() method returns the Unicode normalization form of the string. This is essential for comparing strings that may look identical but have different character compositions—like characters with accents that can be represented as single characters or as a base character plus combining marks.

Syntax

str.normalize([form])

Parameters

Parameter	Type	Default	Description
form	string	"NFC"	The Unicode normalization form: "NFC", "NFD", "NFKC", or "NFKD"

Normalization Forms

• NFC (Canonical Decomposition, Canonical Composition) — Default. Composes characters where possible.
• NFD (Canonical Decomposition) — Decomposes characters into their base + combining marks.
• NFKC (Compatibility Decomposition, Canonical Composition) — Similar to NFC but also normalizes compatibility characters.
• NFKD (Compatibility Decomposition) — Most aggressive decomposition.

Examples

Basic normalization with NFC

const str1 = "\u00E9"; // é as single character
const str2 = "e\u0301"; // e + combining acute accent

console.log(str1 === str2);
// false — they're visually identical but different code points

console.log(str1.normalize() === str2.normalize());
// true — normalize() makes them equal

Comparing user input

function normalizeInput(input) {
  return input.normalize("NFC");
}

const user1 = normalizeInput("café");
const user2 = normalizeInput("café");

console.log(user1 === user2);
// true — works even if user typed differently

Using NFD for character analysis

const str = "résumé";

// NFC: keeps composed form
console.log(str.normalize("NFC").length);
// 6

// NFD: decomposes into base + combining marks  
console.log(str.normalize("NFD").length);
// 8 (é becomes e + ́)

Searching within normalized strings

const words = ["café", "resume", "naïve"];

// Normalize both the search term and array elements
const searchTerm = "CAFÉ".toLowerCase().normalize("NFC");

const found = words.find(w => 
  w.normalize("NFC").toLowerCase() === searchTerm
);

console.log(found);
// "café"

Common Patterns

Form selection guidelines:

• Use NFC for most cases—it’s what users expect and matches most text formats
• Use NFD when you need to count or manipulate individual character components
• Use NFKC/NFKD when dealing with legacy compatibility characters (like ligatures)

Database storage: Always normalize before storing Unicode strings to ensure consistent matching.

Search/compare: Normalize both strings before comparison to handle user variations gracefully.

See Also

• string::at
• string::includes
• string::slice