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tough-cookie.canonicaldomain.md

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Home > tough-cookie > canonicalDomain

canonicalDomain() function

Transforms a domain name into a canonical domain name. The canonical domain name is a domain name that has been trimmed, lowercased, stripped of leading dot, and optionally punycode-encoded (Section 5.1.2 of RFC 6265). For the most part, this function is idempotent (calling the function with the output from a previous call returns the same output).

Signature:

export declare function canonicalDomain(domainName: Nullable<string>): string | undefined;

Parameters

Parameter

Type

Description

domainName

Nullable<string>

the domain name to generate the canonical domain from

 **Returns:**

string | undefined

Remarks

A canonicalized host name is the string generated by the following algorithm:

  1. Convert the host name to a sequence of individual domain name labels.

  2. Convert each label that is not a Non-Reserved LDH (NR-LDH) label, to an A-label (see Section 2.3.2.1 of [RFC5890] for the former and latter), or to a "punycode label" (a label resulting from the "ToASCII" conversion in Section 4 of [RFC3490]), as appropriate (see Section 6.3 of this specification).

  3. Concatenate the resulting labels, separated by a %x2E (".") character.

Example

canonicalDomain('.EXAMPLE.com') === 'example.com'