Question

I’m using coffeescript to create the following class:

class User
  userId: 0
  rooms: new Array()

When I create a new instance of the class and add something to the array, any new instance also contains the same array. The generated javascript is:

  var User;

  User = (function() {

    User.name = 'User';

    function User() {}

    User.prototype.userId = 0;

    User.prototype.rooms = new Array();

    return User;

  })();

How do I design the class that has a new empty array every time I instantiate the class?

Answer 1

You want userId and rooms to be on this, not on the prototype, or else all instances will share them.

class User
  constructor: (@userId = 0, @rooms = []) ->

u = new User 1, [1,2]
u2 = new User 2, [3,4]

alert "#{ u.userId } #{ u.rooms } #{u2.userId} #{u2.rooms}"

Try it here.

The @ simply means this..

The constructor line does a lot. It defines a constructor that

1) sets the passed values as userId and rooms on the object (not the prototype)
2) gives a default value for each property if they are not provided.

Note I didn’t even have to do anything else in the constructor. Definitely follow the link so you can see the javascript this example creates.