Question

I’m trying to figure out how inheritance works in coffeescript. Here’s a simplified example of my code:

class Parent

  constructor: (attrs) ->
    for own name,value of attrs
      this[name] = value

Parent.from_json_array = (json, callback) ->
  for item in JSON.parse(json)
    obj = new ChildA item  # [1]
    callback obj

class ChildA extends Parent

class ChildB extends Parent

ChildA.from_json_array("[{foo: 1}, {foo: 2}]") (obj) ->
  console.log obj.foo

What do I need to put on the line marked [1] to use the correct child class here? This works, but only creates objects with a prototype of ChildA. I’ve tried something like:

Parent.from_json_array = (json, callback) ->
  klass = this.prototype
  for item in JSON.parse(json)
    obj = klass.constructor item  # [1]
    callback obj

… but this leaves obj as undefined in my callback function (TypeError: Cannot read property ‘foo’ of undefined”.

Whats the magic incantation in CoffeeScript to be able to create a new object of a class, where the class is variable?

Answer 1

Nevermind, I figured it out:

Parent.from_json_array = (json, callback) ->
  klass = this
  for item in JSON.parse(json)
    obj = new klass item
    callback obj

Turns out you can just new a class stored in a variable. I thought I had tried this before, but was getting a syntax error.