There are multiple ways for installing this library:

You can install the library by downloading the distributed package and including them on your scripts. Go to Downloads page

If you have npm, you can install the library by running the command (recommended):
npm install --save mp3tag.js@latest

The source codes are written as an ES6 module so you can just copy the src folder and include them on your scripts as module
<script src="/path/to/mp3tag.mjs" type="module">

You can also use CDN services such as UNPKG by including this line on your codes:
<script src="http://unpkg.com/mp3tag.js/dist/mp3tag.min.js">

Changes

save()

save method default options are changed:

id3v1.include is set to false id3v2.unsynch is set to false id3v2.footer support is dropped

mp3tag.errorCode

mp3tag.errorCode was removed (use mp3tag.error instead)

mp3tag.tags

All ID3v2 tags (TIT2, TPE1, ...) are moved to mp3tag.tags.v2