RFC: compiler could prioritize using let over var in compiled JS code.

[barca]

I could be wrong, but I believe that OCaml's variable scoping more closely aligns with javascript's, let than var. I noticed that the code generated by the compiler in the comments uses var exclusively. I'd love to hear other people's thoughts on the matter.

[jordwalke]

JavaScript's const is closer to a true let binding, fwiw.

[barca]

Agreed, but I figured it would be an easier change from var to let

[bobzhang]

I do keep in mind that using let instead of var in the future, there are two reasons not using let yet,

1. there is performance issues, var is more efficient based on my observation
2. not every js engine support let

[davedx]

Yeah, browser support is shaky for now: http://caniuse.com/#search=let

I don't see compilers emitting ES6 for a while yet personally.

@bobzhang are you sure it is still the case that using const or let is slower if you also do minification, etc? I would expect that at least in the case of google closure it would be able to produce better code (more optimizations) if the input uses const and let.

[bobzhang]

There other use cases when you don't want to go through minifier, e.g, NodeJS. I agree Google Closure is a very smart compiler, but only Google Closure does a good job, I once looked at code generated by Babel, which is not as good. Once ES6 is generally optimized, we will revisit this issue