All files / media_types / type_by_extension.ts

// Copyright 2018-2025 the Deno authors. MIT license.
// This module is browser compatible.

import { types } from "./_db.ts";

/**
 * Returns the media type associated with the file extension, or `undefined` if
 * no media type is found.
 *
 * Values are normalized to lower case and matched irrespective of a leading
 * `.`.
 *
 * @param extension The file extension to get the media type for.
 *
 * @returns The media type associated with the file extension, or `undefined` if
 * no media type is found.
 *
 * @example Usage
 * ```ts
 * import { typeByExtension } from "@std/media-types/type-by-extension";
 * import { assertEquals } from "@std/assert";
 *
 * assertEquals(typeByExtension("js"), "text/javascript");
 * assertEquals(typeByExtension(".HTML"), "text/html");
 * assertEquals(typeByExtension("foo"), undefined);
 * assertEquals(typeByExtension("file.json"), undefined);
 * ```
 */
export function typeByExtension(extension: string): string | undefined {
  extension = extension.startsWith(".") ? extension.slice(1) : extension;
  // @ts-ignore Work around https://github.com/denoland/dnt/issues/148
  return types.get(extension.toLowerCase());
}