Question

Here is my coffeescript code.

class Hello
  constructor: ->
    @greetings()
    this.greetings()
    greetings()

  greetings: ->
    alert 'hello world'

new Hello

This code translates into

var Hello;

Hello = (function() {

  function Hello() {
    this.greetings();
    this.greetings();
    greetings();
  }

  Hello.prototype.greetings = function() {
    return alert('hello world');
  };

  return Hello;

})();

new Hello;

In the third case in the coffeescript code I neither used @ nor this. I was assuming that coffeescript would use implicit this but that does not seem to the case.

I did a quick google search but did not get any result. So can anyone confirm that coffeescript does not support implicit this.

Answer 1

Coffeescript does not support implicit this. Mostly because coffee script is really just sugar for javascript, and in javascript this would be a very bad idea, given that functions are first class objects and can be assigned to local variables.

How would access local variables then?

a = -> 123
@a = -> 456

// normal coffeescript
a() # 123

// with implicit this
a() # 123 or 456? Impossible to know.

It important to remember that in java script var a; and this.a have no relation to each other and are always 2 separate variables. Knowing when you are addressing which is really important.

Lastly, this is why the @ notation was created. When using a class based style in javascript it becomes very common to reference properties of this with this.propName all over the place. @ was added to coffee script be less tedious and annoying when programming in this fashion.