chrome extension: How to handle expensive calculations?

I am new to writing chrome extensions and now trying to realize one. Therefore I use a content script to manipulate the current tabs DOM tree.

Within this I am making some calculations that take some time. As a result, the browser is busy until that process ends.

My question is, if there is a possibility to keep the browser going while the calculation is done in the background.

Sorry if this sounds noobish. I am a noob with this topic.

Thank you! :)