Enumerables

In order for Ember to observe when you make a change to an enumerable, you need to use special methods that Ember.Enumerable provides. For example, if you add an element to an array using the standard JavaScript method push, Ember will not be able to observe the change, but if you use the enumerable method pushObject, the change will propagate throughout your application.

Here is a list of standard JavaScript array methods and their observable enumerable equivalents:

Additionally, to retrieve the first and last objects in an array in an observable fashion, you should use myArray.get('firstObject') and myArray.get('lastObject'), respectively.

In the rest of this guide, we'll explore some of the most common enumerable conveniences. For the full list, please see the Ember.Enumerable API reference documentation.

To enumerate all the values of an enumerable object, use the forEach method:

var food = ['Poi', 'Ono', 'Adobo Chicken'];

food.forEach(function(item, index) {
  console.log(`Menu Item ${index+1}: ${item}`);
});

// Menu Item 1: Poi
// Menu Item 2: Ono
// Menu Item 3: Adobo Chicken

All enumerables expose firstObject and lastObject properties that you can bind to.

var animals = ['rooster', 'pig'];

animals.get('lastObject');
//=> "pig"

animals.pushObject('peacock');

animals.get('lastObject');
//=> "peacock"

You can easily transform each item in an enumerable using the map() method, which creates a new array with results of calling a function on each item in the enumerable.

var words = ['goodbye', 'cruel', 'world'];

var emphaticWords = words.map(function(item) {
  return item + '!';
});
// ["goodbye!", "cruel!", "world!"]

If your enumerable is composed of objects, there is a mapBy() method that will extract the named property from each of those objects in turn and return a new array:

var hawaii = Ember.Object.create({
  capital: 'Honolulu'
});

var california = Ember.Object.create({
  capital: 'Sacramento'
});

var states = [hawaii, california];

states.mapBy('capital');
//=> ["Honolulu", "Sacramento"]

Another common task to perform on an enumerable is to take the enumerable as input, and return an Array after filtering it based on some criteria.

For arbitrary filtering, use the filter method. The filter method expects the callback to return true if Ember should include it in the final Array, and false or undefined if Ember should not.

var arr = [1,2,3,4,5];

arr.filter(function(item, index, self) {
  return item < 4;
})

// returns [1,2,3]

When working with a collection of Ember objects, you will often want to filter a set of objects based upon the value of some property. The filterBy method provides a shortcut.

Todo = Ember.Object.extend({
  title: null,
  isDone: false
});

todos = [
  Todo.create({ title: 'Write code', isDone: true }),
  Todo.create({ title: 'Go to sleep' })
];

todos.filterBy('isDone', true);

// returns an Array containing only items with `isDone == true`

If you want to return just the first matched value, rather than an Array containing all of the matched values, you can use find and findBy, which work just like filter and filterBy, but return only one item.

To find out whether every item in an enumerable matches some condition, you can use the every method:

Person = Ember.Object.extend({
  name: null,
  isHappy: false
});

var people = [
  Person.create({ name: 'Yehuda', isHappy: true }),
  Person.create({ name: 'Majd', isHappy: false })
];

people.every(function(person, index, self) {
  return person.get('isHappy');
});

// returns false

To find out whether at least one item in an enumerable matches some condition, you can use the any method:

people.any(function(person, index, self) {
  return person.get('isHappy');
});

// returns true

Just like the filtering methods, the every and any methods have analogous isEvery and isAny methods.

people.isEvery('isHappy', true) // false
people.isAny('isHappy', true)  // true