I have a requirement to download multiple files from server and zip them into one file. So that user will to deal with only one file while downloading.
We have files hosted in akamai servers, we want to download those files in client side, then zip them programatically and popup message asking user where they want to save the zip file.
You contradict yourself. Initially you say that you want your users to deal with just 1 file while downloading. It means that files are ziped up on the server side and downloaded as one big zip files. This makes sense. User saves bandwidth and has to deal with just 1 file downloaded from your site. Plus all files are stored together as a package.
Then you say that you want to download all files separately and zip them up on the client side. This is a completely different requirement and to tell the truth it doesn't make sense to me. The files have already been downloaded. The bandwidth was already consumed. Why would you want to zip them now? You want to popup a message asking where to save this zip file? But the file has already been downloaded. What would you do if user cancels this dialog?
So, the first scenario can be implemented relatively easily. The second scenario (client-side) cannot be implemented with Javscript only. You can do it with an additional help of ActiveX but it will work in IE only.