Question

function abc() {
    var a = 1;
    var func = function() {
        var a = 2;
    }
    func();
    alert(a);
}

Pay attention to the var, in the piece of code, the result of a will be 1, but if the var is omitted, the result will be 2, but I found Coffee not able to translate to this.

For example the following:

abc = ->
    a = 1
    func = ->
        a = 2
        return
    func()
    alert(a)
    return

Answer 1

CoffeeScript, by design, doesn’t allow you to shadow a previously declared variable. Yet, there is one case where it still happens:

abc = ->
    a = 1
    func = (a) ->
        a = 2
        return
    func()
    alert(a)
    return

That will result in a 1. Because a is function parameter, it’s local to the function scope.

BTW, you could rewrite this as

abc = ->
    a = 1
    do (a) -> a = 2
    alert a
    return

where do (a) -> a = 2 is equivalent to ((a) -> a = 2)().