MIME Type Parsing

undici exposes helpers for parsing and serializing MIME types according to the WHATWG MIME Sniffing Standard. These are the same primitives undici uses internally to interpret Content-Type headers and data: URLs.

Import the functions from 'undici':

import { parseMIMEType, serializeAMimeType } from 'undici'

A parsed MIME type is represented as a plain object with the following shape:

parseMIMEType(input): Object | string

Implements the WHATWG parse a MIME type algorithm. The type and subtype are lowercased, and only the first occurrence of a duplicate parameter name is retained. When input is empty, lacks a /, or otherwise violates the grammar, the string literal 'failure' is returned instead of a record.

import { parseMIMEType } from 'undici'

parseMIMEType('text/html; charset=gbk')
// {
//   type: 'text',
//   subtype: 'html',
//   parameters: Map(1) { 'charset' => 'gbk' },
//   essence: 'text/html'
// }

parseMIMEType('not a mime type')
// 'failure'

serializeAMimeType(mimeType): string

Implements the WHATWG serialize a MIME type algorithm. The essence is emitted followed by each parameter as ;name=value. A parameter value that contains characters outside the HTTP token set is quoted, and any " or \ characters within it are escaped.

import { serializeAMimeType } from 'undici'

serializeAMimeType({
  type: 'text',
  subtype: 'html',
  parameters: new Map([['charset', 'gbk']]),
  essence: 'text/html'
})
// 'text/html;charset=gbk'