Objects chaining interrogations

Question

I spent some time on something I thought was a bug until I found a workaround.

Still I can't understand why the previous code failed.

Any insight please?

Failing code:

getModule: ->
  Gmaps4Rails.Google

createMap : ->
  new @getModule().Map()

Working code:

constructor:
  @module = @getModule()

getModule: ->
  Gmaps4Rails.Google

createMap : ->
  new @module.Map()

Answer 1

The reason is that new anonymous function is not the same as new Gmaps4Rails.Google() in JavaScript.

// Translated JavaScript code (simplified):

var your_module = {
    getModule: function() {
        return Gmaps4Rails.Google;
    },
    createMap: function() {
        // This is where things go wrong
        return new this.getModule().Map();
    }
};

The problem is that return new this.getModule().Map(); translates to return new function() { return Gmaps4Rails.Google; } - which ignores the return value and uses this (which is a new object inheriting from the anonymous function). Thus the line essentially translates to return {}.Map(); Since objects do not have a Map method, you get an error.

When you set @module to be a reference to Gmaps4Rails.Google then when you call new @module.Map() you are actually calling new Gmaps4Rails.Google - and it returns an object which has a Map method - thus everything works.