mrmime

Common errors

• TypeError: (0 , mrmime_1.lookup) is not a function

  cause Attempting to use CommonJS `require` with named imports incorrectly in an environment expecting ES modules, or vice-versa.
  fix If using `require`, use `const { lookup } = require('mrmime');`. If in an ES module environment, ensure `import { lookup } from 'mrmime';` is used and the file is treated as an ES module (e.g., `.mjs` extension or `type: 'module'` in `package.json`).

• MIME type not found for '.xyz'

  cause Looking up an extension that is not present in `mrmime`'s internal dictionary, which will result in `lookup` returning `undefined`.
  fix Recognize that `lookup` returns `undefined` for unknown extensions. If the extension is valid for your application, add it to the `mimes` dictionary: `mimes['xyz'] = 'your/custom-type';`.

Warnings

• breaking The `lookup` function's return signature changed from `string | void` to `string | undefined` in v2.0.0. This aligns with TypeScript's `undefined` type for missing values.
  Fix: Update type assertions or nullish coalescing logic to explicitly check for `undefined` instead of `void`.
• breaking Upgrading to `mrmime` v2.0.0 includes an updated `mime-db` version, which resulted in changes to some extension-to-MIME-type mappings. Specifically, the `es` extension was removed, and others like `asc` had their values changed. Review the full changelog for details.
  Fix: Verify that expected MIME types for specific extensions are still correct after upgrading. If a previously recognized type is now `undefined` or changed, update application logic or manually add/override the type in the `mimes` dictionary.
• gotcha In `mrmime` versions up to `v1.0.0`, TypeScript 4.7+ environments might not correctly discover the type definitions. This was fixed in `v1.0.1` by adding the 'types' export condition.
  Fix: Upgrade to `mrmime` v1.0.1 or newer to ensure correct TypeScript type discovery.

Install

• npm install mrmime npm
• yarn add mrmime yarn
• pnpm add mrmime pnpm

Imports

• lookup
  wrong:

  const lookup = require('mrmime').lookup;

  correct:

  import { lookup } from 'mrmime';

  Primarily designed for ESM. While CommonJS works, named imports are preferred.
• mimes
  wrong:

  const mimes = require('mrmime').mimes;

  correct:

  import { mimes } from 'mrmime';

  The `mimes` object allows for runtime additions or overrides of MIME types and is mutable.
• mrmime (CommonJS destructuring)

  const { lookup, mimes } = require('mrmime');

  For CommonJS environments, destructuring the require call is the idiomatic way to access named exports.

Quickstart

Demonstrates how to lookup MIME types for various inputs, handle unknown extensions, and dynamically customize the internal MIME dictionary.

import { lookup, mimes } from 'mrmime';

// Get a MIME type from an extension or filename
console.log(lookup('txt'));     // => "text/plain"
console.log(lookup('.txt'));    // => "text/plain"
console.log(lookup('a.txt'));   // => "text/plain"
console.log(lookup('index.html')); // => "text/html"

// Handle unknown extensions (returns undefined since v2.0.0)
console.log(lookup('.xyz'));    // => undefined

// Customize the MIME dictionary by adding a new type
mimes['xyz'] = 'hello/world';
console.log(lookup('xyz'));     // => "hello/world"

// Example with a common file type check
const filename = 'document.pdf';
const mimeType = lookup(filename);
if (mimeType) {
  console.log(`The MIME type for '${filename}' is: ${mimeType}`);
} else {
  console.log(`Could not determine MIME type for '${filename}'.`);
}