Reopening Classes and Instances

You don't need to define a class all at once. You can reopen a class and define new properties using the reopen method.

Person.reopen({
  isPerson: true
});

Person.create().get('isPerson') // true

When using reopen, you can also override existing methods and call this._super.

Person.reopen({
  // override `say` to add an ! at the end
  say: function(thing) {
    this._super(thing + "!");
  }
});

reopen is used to add instance methods and properties that are shared across all instances of a class. It does not add methods and properties to a particular instance of a class as in vanilla JavaScript (without using prototype).

But when you need to add static methods or static properties to the class itself you can use reopenClass.

// add static property to class
Person.reopenClass({
  isPerson: false
});
// override property of Person instance
Person.reopen({
  isPerson: true
});

Person.isPerson; // false - because it is static property created by `reopenClass`
Person.create().get("isPerson"); // true