Ember.observerOnce - combines Ember.observer + Ember.run.once

observerOnce.js

//
// Example: http://jsbin.com/welusizema/1/edit
//
// Since observers are not async, it's usually a good
// practice, when observing numerous properties, to
// wrap the observer function with an Ember.run.once.
// ```
// fooBarChanged: Ember.observer('foo', 'bar', function () {
//   Ember.run.once(this, this.scheduledChange);
// }),
// scheduledChange: function () {
//   console.log('Will only be invoked once if foo and bar are changed within the same runloop');
// }
// ```
// This just removes having to create two functions, one for the sole purpose of
// invoking Ember.run.once.
//
// The above code would now become:
// ```
// fooBarChanged: Ember.observerOnce('foo', 'bar', function () {
//   console.log('Will only be invoked once if foo and bar are changed within the same runloop');
// })
// ```
Ember.observerOnce = function observeOnce () {
  var a_slice = [].slice;
  var func = a_slice.call(arguments, -1)[0];
  if (typeof func !== 'function') {
    throw new Ember.Error("Ember.observer called without a function");
  }
  var paths = a_slice.call(arguments, 0, -1);
  var out = function () {
    Ember.run.once(this, func);
  }
  out.__ember_observes__ = paths;
  return out;
}