A simple JSON stringify function which requires Array.prototype.map method.
The following users provided lots of ideas and improvements of the code.
@Kambfhase, @hartrock, @atk, @haochi, @jed
Actually, I just provided a deficient version at first. The other versions were created by these users(especially @atk). You may see the discussion below.
It was obvious to us that the contents of strings are not correctly escaped, so we didn't mention it. We're still in the process of golfing for more space for the necessary filter.