Ember.js how does reopenClass work?

Question

I don\'t really get the function of ember.js\' reopenClass. I thought it added extra code to the Object\'s prototype, so all instances of that Object would get the functiona

Answer 1

In general, reopen adds methods and properties to instances whereas reopenClass adds methods and properties to classes.

The corresponding tests are ember-runtime/tests/system/object/reopen_test.js and packages/ember-runtime/tests/system/object/reopenClass_test.js.

I've updated your code and added some comments, see http://jsfiddle.net/pangratz666/yWKBF/:

Logger = Ember.Object.extend({
    log: function(thing) {
        console.log(thing + ' wassup');
    }
});

var logger1 = Logger.create();
var logger2 = Logger.create();

// instances of Logger have a 'wassup' method
try { Logger.log("1, yo"); } catch (e) {} // Object (subclass of Ember.Object) has no method 'log'
logger1.log("1, yo"); // 1, yo wassup
logger2.log("1, yo"); // 1, yo wassup

console.log('----');

// overwrite log of concrete logger instance logger1
logger1.reopen({
    log: function(name) {
        console.log(name + ' ghurt');
    }
});

try { Logger.log("1, yo"); } catch (e) {} // Object (subclass of Ember.Object) has no method 'log'
logger1.log("2, yo"); // 2, yo ghurt
logger2.log("2, yo"); // 2, yo wassup

console.log('----');

// classes of Logger have a 'fresh' method
Logger.reopenClass({
    log: function(name) {
        console.log(name + ' fresh');
    }
});

Logger.log("3, yo"); // 3, yo fresh
logger1.log("3, yo"); // 3, yo ghurt
logger2.log("3, yo"); // 3, yo wassup

console.log('----');

// new* instances of Logger have from now on a 'dawg' method
// * this will likely change in the future so already existing instances will reopened too
Logger.reopen({
    log: function(name) {
        console.log(name + ' dawg');
    }
});

Logger.log("4, yo"); // 4, yo fresh
logger1.log("4, yo"); // 4, yo ghurt
logger2.log("4, yo"); // 4, yo wassup
Logger.create().log("4, yo"); // 4, yo dawg

console.log('----');

​

Answer 2

reopen changes prototype and thus changes instances of a class

reopenClass changes the constructor itself and thus changes the class by creating static properties and functions that are only available on the class but not on any instances of the class.

Note that the changes introduced by reopen only take effect after calling .create()

Code examples based on the doc:

http://emberjs.com/api/classes/Ember.Application.html#method_reopen

MyObject = Ember.Object.extend({
  name: 'an object'
});

o = MyObject.create();
o.get('name'); // 'an object'

MyObject.reopen({
  say: function(msg){
    console.log(msg);
  }
})

try{
    o.say("hey");
} catch(e) {
    console.log(e); // o.say is not a function (...yet)
}
o2 = MyObject.create();
o2.say("hello"); // logs "hello"

o.say("goodbye"); // logs "goodbye"

http://emberjs.com/api/classes/Ember.Application.html#method_reopenClass

MyObject = Ember.Object.extend({
  name: 'an object'
});

MyObject.reopenClass({
  canBuild: false
});

MyObject.canBuild; // false
o = MyObject.create();
o.canBuild; // undefined