Question

I’m using the following code in CoffeeScript:

if elem in my_array
  do_something()

Which compiles to this javascript:

if (__indexOf.call(my_array, elem) < 0) {
  my_array.push(elem);
}

I can see it’s using the function __indexOf which is defined at the top of the script.

My question is regarding this use case: I want to remove an element from an array, and I want to support IE8. I can do that easily with indexOf and splice in browsers who support indexOf on an array object. However, in IE8 this doesn’t work:

if (attr_index = my_array.indexOf(elem)) > -1
  my_array.splice(attr_index, 1)

I tried using the __indexOf function defined by CoffeScript but I get a reserved word error in the compiler.

if (attr_index = __indexOf.call(my_array, elem) > -1
  my_array.splice(attr_index, 1)

So how can I use CoffeScript or is there a more unobtrusive method for calling indexOf? It seems weird to define the same function twice, just because CoffeeScript won’t let me use theirs…

Answer 1

No, CoffeeScript precludes you from using its helpers directly, since that would break down the distinction between the language and the implementation. To support IE8, I would add a shim like

Array::indexOf or= (item) ->
  for x, i in this
    return i if x is item
  return -1

or use a library like Underscore.js for array manipulation.