Actually I don't understand why we include JS in html .

Question

I didn't mean why we use javascript in html without using it individually.I meant why we include some of JS in html5 in the <canvas> tag.

Answer 1

Probably because html is a markup language and not a programming language.

The canvas itself needs to be programmed so that's why it needs javascript.

If we would use html5 and css instead I'm afraid it would limit the possibilities we have with the canvas tag.

Edit: if you look up some canvas demos you would find awesome creations. These simply can't be made with standard html.