@j.arunmani
I haven’t used DevHelp yet, so not sure if it will allow you to search the docsets like Zeal does. You should be able to open them up in DevHelp but it may not work with the quick search features.

If you decide to use Zeal again, I need to mention that the Javascript docset does not have a landing page like HTML and CSS. So you can’t access the Learning Section normally.
If you are using Linux, here are two options you might try.

You can use a modified landing page that contains links to the learning modules and other useful pages. I provide instructions here on how to do that.

A second option, you can go to this folder in the Zeal docsets on your computer. It contains the files for the Learning Section.

/home/<yourcomputernamehere>/.local/share/Zeal/Zeal/docsets/JavaScript.docset/Contents/Resources/Documents/developer.mozilla.org/en-US/docs/Learn/JavaScript/

(Note where it says <yourcomputernamehere> , that is where you should put your computer name.)

Another option is to use a website downloader to get everything at this url here. When using whichever downloader you choose, there should be some kind of option to keep that link as the root of download, meaning that it shouldn’t download the whole MDN site, only subpaths of .../Learn such as .../Learn/CSS or .../Learn/Javascript.

I typically bookmark the index page of a downloaded website. You can use your browser like this with the Zeal docsets as well. When using Zeal, you can right click and open that page in the your browser, then bookmark it in the browser.