Navigator.mimeTypes

Returns a MimeTypeArray object, which contains a list of MimeType objects representing the MIME types recognized and supported by the browser. The array can be queried for information about the enabled plugin that is used to handle a file of the specified type. Named properties of the returned object are not enumerable (except in very old browser versions).

Recent versions of the specification hard-code the returned set of MIME types. If PDF files can be displayed inline then application/pdf and text/pdf are listed. Otherwise an empty list is returned.

Legacy browser versions do not hard-code the list returned by the property, and might return other MIME types.

A MimeTypeArray object which has a length property as well as item(index) and namedItem(name) methods.

If PDF inline viewing is supported this has entries for MIME types application/pdf and text/pdf. Otherwise an empty MimeTypeArray is returned. The description and file suffixes supported by enabled plugins are hard coded to 'pdf' and 'Portable Document Format', respectively.

The code below tests whether PDF files can be viewed inline, and then prints the description of the plugin and the file suffixes it supports.

if ('application/pdf' in navigator.mimeTypes) { 
  // browser supports inline viewing of PDF files.

  const { description, suffixes } = navigator.mimeTypes['application/pdf'];
  console.log(`Description: ${ description }, Suffix: ${ suffixes }`);
  // expected output: Description: Portable Document Format, Suffix: pdf
}

Note that while the above code tests for application/pdf you could equally well check text/pdf. (Either both or neither MIME type will be true.) In addition, on current browsers you don't actually need to get the plugin description and suffixes, because this information is also hard-coded.