I don't think there would be much benefit except possibly some minor performance gains. But then to even take advantage of these you would likely have to be extremely proficient in native JS.

Personally, I don't really see much of a downside to JS transpiled languages. You are already working with a high-level scripting language. The incredible amount of benefits you gain from using something like Coffeescript or Typescript far exceed any negligible downside to them.

(You do have to trust that the transpiled language is good however. You don't want to accidentally start using a bad language that fails to transpile or is simply harder to work with than native js. With Coffeescript/Typescript being very popular, I would consider them both "safe".)

If you don't know JS really well, I wouldn't recommend Coffeescript. It's hard to tell what will work correctly and what won't unless you're quite familiar with the actual code the Coffeescript is compiling down to. I don't know how true this is for other transpiling languages, but it's definitely true for Coffeescript.

I'm a pretty experienced JS dev, so I know exactly what my CS is compiling to and what that's going to do. If I didn't, CS would make me tear my hair out within a week. As it is, it's just shorthand for JS with a bunch of quality of life improvements (?, no var, etc).

This is a good post by wycats that discusses this:

https://meta.discourse.org/t/is-it-better-for-discourse-to-u...