Enumerables Edit Page


In Ember.js, an enumerable is any object that contains a number of child objects, and which allows you to work with those children using the Ember.Enumerable API. The most common enumerable in the majority of apps is the native JavaScript array, which Ember.js extends to conform to the enumerable interface.

By providing a standardized interface for dealing with enumerables, Ember.js allows you to completely change the way your underlying data is stored without having to modify the other parts of your application that access it.

The enumerable API follows ECMAScript specifications as much as possible. This minimizes incompatibility with other libraries, and allows Ember.js to use the native browser implementations in arrays where available.

Use of Observable Methods and Properties

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:

Standard MethodObservable Equivalent
poppopObject
pushpushObject
reversereverseObjects
shiftshiftObject
unshiftunshiftObject

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.

API Overview

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.

Iterating Over an Enumerable

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

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

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

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

First and Last Objects

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

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

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

animals.pushObject('peacock');

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

Map

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.

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

let emphaticWords = words.map(item => `${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:

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import EmberObject from '@ember/object';

let hawaii = EmberObject.create({
  capital: 'Honolulu'
});

let california = EmberObject.create({
  capital: 'Sacramento'
});

let states = [hawaii, california];

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

Filtering

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.

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

arr.filter((item, index, self) => item < 4);

//=> [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.

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import EmberObject from '@ember/object';

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

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

Aggregate Information (Every or Any)

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

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import EmberObject from '@ember/object';

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

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

people.every((person, index, self) => person.get('isHappy'));

//=> false

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

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people.any((person, index, self) => person.get('isHappy'));

//=> true

Like the filtering methods, the every() and any() methods have analogous isEvery() and isAny() methods.

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