How to keep animated gif running while doing intense calculations

Question

I have a page which does some intense and long lasting calculations in Javascript. I would like to have a loading animation to tell the user progress is being made. I have a

Answer 1

CSS3 animations typically continue running even if JavaScript is blocking (tested with Chrome 40.0).

So you can use libraries like SpinKit or spin.js to visualize that the calculation is ongoing.

However, note the availability of CSS3 animations:
caniuse.com
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