WebStorm is not highlighting JS code

Question

WebStorm is not highlighting properly JS code whether its in HTML file or in JS file. It says unresolved variable or type document when I want to get ID of element using document.getElementByiD.

I have also captured settings

Answer 1

3 Things to try:

1. Try File | Invalidate Caches and restart IDE. (credits @LazyOne)
2. File -> Settings > Editor -> File Types, select JavaScript into list of file types and check if you have *.js into list of extensions below. Alternatively try to create new draft (Shift+Ctrl+Alt+Ins) for JavaScript language and take a look if it get highlighted. (credits @Flying)
3. Go to File | Settings | Languages & Frameworks | JavaScript and Choose ECMAScript 5.1 and press ok. Files shoud now be highlighted correctly. Then, open the menu again and re-select ECMAScript 6+.