If you’ve ever considered learning JavaScript, started to learn JavaScript, or you are a seasoned JavaScript veteran, Mozilla has a great resource for you!
MDN Learning offers:
… a variety of JavaScript tutorials and JavaScript training materials. Whether you are just starting out, wanting to learn JS basics, or are an old hand, wanting to sharpen your skills, you can find helpful resources here for JS best practices.
MDN has broken it down into three sections: Introductory, Intermediate, and Advanced.