Exporting fbx file with webgl

Hi, I want to make a HTML5 application which allows users to create their own character and download it from the presets available.

Is it possible to write code to export a completed 3d character model in fbx(or obj) format, that the user can download?

I tried it with three.js but no luck.

I basically want to throw in a few morphs and let the user select the features he want for the character and he can merge them as he likes(or write a script in c# which randomly generates a game ready model within the browser). Now the user must be able to download through the browser.

If this is not possible, I could go for a standalone app for pc or mac or even an android application to let users download the customized model.