Question

In coffee script, using the existential operator on a function like so:

myFunc?()

compiles to

typeof myFunc === "function" ? myFunc() : void 0;

Is there a way to elegantly define what would go in place of “void 0”? or must I write it all out instead of using the original notation?

Answer 1

You can add another existential operator:

x = f?() ? 'pancakes'

That won’t work if f() returns null or undefined but it will do the Right Thing if f() returns false. For example:

f = 'not a function'
console.log f?() ? 'pancakes'
# pancakes

f = -> 'is a function'
console.log f?() ? 'pancakes'
# is a function

f = -> null
console.log f?() ? 'pancakes'
# pancakes

f = ->
console.log f?() ? 'pancakes'
# pancakes

f = -> false
console.log f?() ? 'pancakes'
# false

Demo: http://jsfiddle.net/ambiguous/f6yvN/1/

So you can get close to what you want and that might be close enough depending on what sort of things you’re expecting the function to return.