RangeError: form must be one of 'NFC', 'NFD', 'NFKC', or 'NFKD'

The JavaScript exception "form must be one of 'NFC', 'NFD', 'NFKC', or 'NFKD'" occurs when an unrecognized string is passed to the String.prototype.normalize() method.

Message

RangeError: The normalization form should be one of NFC, NFD, NFKC, NFKD. (V8-based)
RangeError: form must be one of 'NFC', 'NFD', 'NFKC', or 'NFKD' (Firefox)
RangeError: argument does not match any normalization form (Safari)

Error type

What went wrong?

The String.prototype.normalize() method only accepts the following four values as its form argument: "NFC", "NFD", "NFKC", or "NFKD". If you pass any other value, an error will be thrown. Read the reference of normalize() to learn about different normalization forms.

Examples

Invalid cases

"foo".normalize("nfc"); // RangeError
"foo".normalize(" NFC "); // RangeError

Valid cases

"foo".normalize("NFC"); // 'foo'

See also

• String.prototype.normalize()