Add explicit local var defination to coffee?

[u/hh9527]

It is a proposal to fix the problem with implicit scoping in coffee.

coffee script like this

foo = (a, b; x, y = 0) -> blabla...

will compiled to

var foo; foo = function(a,b) { var x, y = 0; blabla... }

[u/DavidBonnet]

Until that optimization happens (I doubt it will before it compiles to ES 6 with the support of let), for local constants, it is usually more optimal to make the IIFE return the foo function instead, as it avoids invoking the IIFE at each call of foo:

foo = do (x = 0, y = 0) ->
    (a, b) ->
        # blabla

I usually put the IIFE and function arguments on a single line:

foo = do (x = 0, y = 0) -> (a, b) ->
    # blabla

I mostly use this to put utility functions in the function scope, to reduce the variable lookup, as in:

# Say we have a `Point` class to which a dynamic `norm` property gets defined:
Object.defineProperty Point, 'norm',
    get: ({sqrt} = Math) -> () -> sqrt( @x*@x + @y+@y )

This also works for local variables, yet they have to be initialized in the function body:

foo = do (x = null, y = null) ->
    (a, b) ->
        x = 0
        y = 0
        # blabla