Annotating or fetching selected text content using React

I'm trying to build a chrome extension using React and I could not figure out how I can get selected web content into my extension app. I am going to use it for creating annotations on the web content.

To give an example, User visits a web page, selects a text or whole paragraph and the extension will be able to get the content of selected text. I am going to highlight the text and show the user comment then. (e.g. medium.com's annotation model)

I've tried AnnotatorJS but I cannot annotate the content outside of my application context.

What can be the accurate way for implementing annotations in React?