Ember.computed

This helper returns a new property descriptor that wraps the passed computed property function. You can use this helper to define properties with mixins or via Ember.defineProperty().

If you pass a function as an argument, it will be used as a getter. A computed property defined in this way might look like this:

let Person = Ember.Object.extend({
  init() {
    this._super(...arguments);

    this.firstName = 'Betty';
    this.lastName = 'Jones';
  },

  fullName: Ember.computed('firstName', 'lastName', function() {
    return `${this.get('firstName')} ${this.get('lastName')}`;
  })
});

let client = Person.create();

client.get('fullName'); // 'Betty Jones'

client.set('lastName', 'Fuller');
client.get('fullName'); // 'Betty Fuller'

You can pass a hash with two functions, get and set, as an argument to provide both a getter and setter:

let Person = Ember.Object.extend({
  init() {
    this._super(...arguments);

    this.firstName = 'Betty';
    this.lastName = 'Jones';
  },

  fullName: Ember.computed('firstName', 'lastName', {
    get(key) {
      return `${this.get('firstName')} ${this.get('lastName')}`;
    },
    set(key, value) {
      let [firstName, lastName] = value.split(/\s+/);
      this.setProperties({ firstName, lastName });
      return value;
    }
  })
});

let client = Person.create();
client.get('firstName'); // 'Betty'

client.set('fullName', 'Carroll Fuller');
client.get('firstName'); // 'Carroll'

The set function should accept two parameters, key and value. The value returned from set will be the new value of the property.

Note: This is the preferred way to define computed properties when writing third-party libraries that depend on or use Ember, since there is no guarantee that the user will have prototype Extensions enabled.

The alternative syntax, with prototype extensions, might look like:

fullName: function() {
  return this.get('firstName') + ' ' + this.get('lastName');
}.property('firstName', 'lastName')

Creates a new property that is an alias for another property on an object. Calls to get or set this property behave as though they were called on the original property.

let Person = Ember.Object.extend({
  name: 'Alex Matchneer',
  nomen: Ember.computed.alias('name')
});

let alex = Person.create();

alex.get('nomen'); // 'Alex Matchneer'
alex.get('name');  // 'Alex Matchneer'

alex.set('nomen', '@machty');
alex.get('name');  // '@machty'

A computed property that performs a logical and on the original values for the provided dependent properties.

You may pass in more than two properties and even use property brace expansion. The computed property will return the first falsy value or last truthy value just like JavaScript's && operator.

Example

let Hamster = Ember.Object.extend({
  readyForCamp: Ember.computed.and('hasTent', 'hasBackpack'),
  readyForHike: Ember.computed.and('hasWalkingStick', 'hasBackpack')
});

let tomster = Hamster.create();

tomster.get('readyForCamp'); // false
tomster.set('hasTent', true);
tomster.get('readyForCamp'); // false
tomster.set('hasBackpack', true);
tomster.get('readyForCamp'); // true
tomster.set('hasBackpack', 'Yes');
tomster.get('readyForCamp'); // 'Yes'
tomster.set('hasWalkingStick', null);
tomster.get('readyForHike'); // null

A computed property that converts the provided dependent property into a boolean value.

let Hamster = Ember.Object.extend({
  hasBananas: Ember.computed.bool('numBananas')
});

let hamster = Hamster.create();

hamster.get('hasBananas'); // false
hamster.set('numBananas', 0);
hamster.get('hasBananas'); // false
hamster.set('numBananas', 1);
hamster.get('hasBananas'); // true
hamster.set('numBananas', null);
hamster.get('hasBananas'); // false

A computed property that returns the array of values for the provided dependent properties.

Example

let Hamster = Ember.Object.extend({
  clothes: Ember.computed.collect('hat', 'shirt')
});

let hamster = Hamster.create();

hamster.get('clothes'); // [null, null]
hamster.set('hat', 'Camp Hat');
hamster.set('shirt', 'Camp Shirt');
hamster.get('clothes'); // ['Camp Hat', 'Camp Shirt']

Creates a new property that is an alias for another property on an object. Calls to get or set this property behave as though they were called on the original property, but also print a deprecation warning.

let Hamster = Ember.Object.extend({
  bananaCount: Ember.computed.deprecatingAlias('cavendishCount', {
    id: 'hamster.deprecate-banana',
    until: '3.0.0'
  })
});

let hamster = Hamster.create();

hamster.set('bananaCount', 5); // Prints a deprecation warning.
hamster.get('cavendishCount'); // 5

A computed property that returns true if the value of the dependent property is null, an empty string, empty array, or empty function.

Example

let ToDoList = Ember.Object.extend({
  isDone: Ember.computed.empty('todos')
});

let todoList = ToDoList.create({
  todos: ['Unit Test', 'Documentation', 'Release']
});

todoList.get('isDone'); // false
todoList.get('todos').clear();
todoList.get('isDone'); // true

A computed property that returns true if the provided dependent property is equal to the given value.

Example

let Hamster = Ember.Object.extend({
  satisfied: Ember.computed.equal('percentCarrotsEaten', 100)
});

let hamster = Hamster.create();

hamster.get('satisfied'); // false
hamster.set('percentCarrotsEaten', 100);
hamster.get('satisfied'); // true
hamster.set('percentCarrotsEaten', 50);
hamster.get('satisfied'); // false

Filters the array by the callback.

The callback method you provide should have the following signature. item is the current item in the iteration. index is the integer index of the current item in the iteration. array is the dependant array itself.

function(item, index, array);

let Hamster = Ember.Object.extend({
  remainingChores: Ember.computed.filter('chores', function(chore, index, array) {
    return !chore.done;
  })
});

let hamster = Hamster.create({
  chores: [
    { name: 'cook', done: true },
    { name: 'clean', done: true },
    { name: 'write more unit tests', done: false }
  ]
});

hamster.get('remainingChores'); // [{name: 'write more unit tests', done: false}]

Filters the array by the property and value

let Hamster = Ember.Object.extend({
  remainingChores: Ember.computed.filterBy('chores', 'done', false)
});

let hamster = Hamster.create({
  chores: [
    { name: 'cook', done: true },
    { name: 'clean', done: true },
    { name: 'write more unit tests', done: false }
  ]
});

hamster.get('remainingChores'); // [{ name: 'write more unit tests', done: false }]

A computed property that returns true if the provided dependent property is greater than the provided value.

Example

let Hamster = Ember.Object.extend({
  hasTooManyBananas: Ember.computed.gt('numBananas', 10)
});

let hamster = Hamster.create();

hamster.get('hasTooManyBananas'); // false
hamster.set('numBananas', 3);
hamster.get('hasTooManyBananas'); // false
hamster.set('numBananas', 11);
hamster.get('hasTooManyBananas'); // true

A computed property that returns true if the provided dependent property is greater than or equal to the provided value.

Example

let Hamster = Ember.Object.extend({
  hasTooManyBananas: Ember.computed.gte('numBananas', 10)
});

let hamster = Hamster.create();

hamster.get('hasTooManyBananas'); // false
hamster.set('numBananas', 3);
hamster.get('hasTooManyBananas'); // false
hamster.set('numBananas', 10);
hamster.get('hasTooManyBananas'); // true

A computed property which returns a new array with all the duplicated elements from two or more dependent arrays.

Example

let obj = Ember.Object.extend({
  friendsInCommon: Ember.computed.intersect('adaFriends', 'charlesFriends')
}).create({
  adaFriends: ['Charles Babbage', 'John Hobhouse', 'William King', 'Mary Somerville'],
  charlesFriends: ['William King', 'Mary Somerville', 'Ada Lovelace', 'George Peacock']
});

obj.get('friendsInCommon'); // ['William King', 'Mary Somerville']

A computed property that returns true if the provided dependent property is less than the provided value.

Example

let Hamster = Ember.Object.extend({
  needsMoreBananas: Ember.computed.lt('numBananas', 3)
});

let hamster = Hamster.create();

hamster.get('needsMoreBananas'); // true
hamster.set('numBananas', 3);
hamster.get('needsMoreBananas'); // false
hamster.set('numBananas', 2);
hamster.get('needsMoreBananas'); // true

A computed property that returns true if the provided dependent property is less than or equal to the provided value.

Example

let Hamster = Ember.Object.extend({
  needsMoreBananas: Ember.computed.lte('numBananas', 3)
});

let hamster = Hamster.create();

hamster.get('needsMoreBananas'); // true
hamster.set('numBananas', 5);
hamster.get('needsMoreBananas'); // false
hamster.set('numBananas', 3);
hamster.get('needsMoreBananas'); // true

Returns an array mapped via the callback

The callback method you provide should have the following signature. item is the current item in the iteration. index is the integer index of the current item in the iteration.

function(item, index);

Example

let Hamster = Ember.Object.extend({
  excitingChores: Ember.computed.map('chores', function(chore, index) {
    return chore.toUpperCase() + '!';
  })
});

let hamster = Hamster.create({
  chores: ['clean', 'write more unit tests']
});

hamster.get('excitingChores'); // ['CLEAN!', 'WRITE MORE UNIT TESTS!']

Returns an array mapped to the specified key.

let Person = Ember.Object.extend({
  childAges: Ember.computed.mapBy('children', 'age')
});

let lordByron = Person.create({ children: [] });

lordByron.get('childAges'); // []
lordByron.get('children').pushObject({ name: 'Augusta Ada Byron', age: 7 });
lordByron.get('childAges'); // [7]
lordByron.get('children').pushObjects([{
  name: 'Allegra Byron',
  age: 5
}, {
  name: 'Elizabeth Medora Leigh',
  age: 8
}]);
lordByron.get('childAges'); // [7, 5, 8]

A computed property which matches the original value for the dependent property against a given RegExp, returning true if the value matches the RegExp and false if it does not.

Example

let User = Ember.Object.extend({
  hasValidEmail: Ember.computed.match('email', /^.+@.+\..+$/)
});

let user = User.create({loggedIn: false});

user.get('hasValidEmail'); // false
user.set('email', '');
user.get('hasValidEmail'); // false
user.set('email', 'ember_hamster@example.com');
user.get('hasValidEmail'); // true

A computed property that calculates the maximum value in the dependent array. This will return -Infinity when the dependent array is empty.

let Person = Ember.Object.extend({
  childAges: Ember.computed.mapBy('children', 'age'),
  maxChildAge: Ember.computed.max('childAges')
});

let lordByron = Person.create({ children: [] });

lordByron.get('maxChildAge'); // -Infinity
lordByron.get('children').pushObject({
  name: 'Augusta Ada Byron', age: 7
});
lordByron.get('maxChildAge'); // 7
lordByron.get('children').pushObjects([{
  name: 'Allegra Byron',
  age: 5
}, {
  name: 'Elizabeth Medora Leigh',
  age: 8
}]);
lordByron.get('maxChildAge'); // 8

If the types of the arguments are not numbers, they will be converted to numbers and the type of the return value will always be Number. For example, the max of a list of Date objects will be the highest timestamp as a Number. This behavior is consistent with Math.max.

A computed property that calculates the minimum value in the dependent array. This will return Infinity when the dependent array is empty.

let Person = Ember.Object.extend({
  childAges: Ember.computed.mapBy('children', 'age'),
  minChildAge: Ember.computed.min('childAges')
});

let lordByron = Person.create({ children: [] });

lordByron.get('minChildAge'); // Infinity
lordByron.get('children').pushObject({
  name: 'Augusta Ada Byron', age: 7
});
lordByron.get('minChildAge'); // 7
lordByron.get('children').pushObjects([{
  name: 'Allegra Byron',
  age: 5
}, {
  name: 'Elizabeth Medora Leigh',
  age: 8
}]);
lordByron.get('minChildAge'); // 5

If the types of the arguments are not numbers, they will be converted to numbers and the type of the return value will always be Number. For example, the min of a list of Date objects will be the lowest timestamp as a Number. This behavior is consistent with Math.min.

A computed property that returns true if the value of the dependent property is null or undefined. This avoids errors from JSLint complaining about use of ==, which can be technically confusing.

Example

let Hamster = Ember.Object.extend({
  isHungry: Ember.computed.none('food')
});

let hamster = Hamster.create();

hamster.get('isHungry'); // true
hamster.set('food', 'Banana');
hamster.get('isHungry'); // false
hamster.set('food', null);
hamster.get('isHungry'); // true

A computed property that returns the inverse boolean value of the original value for the dependent property.

Example

let User = Ember.Object.extend({
  isAnonymous: Ember.computed.not('loggedIn')
});

let user = User.create({loggedIn: false});

user.get('isAnonymous'); // true
user.set('loggedIn', true);
user.get('isAnonymous'); // false

A computed property that returns true if the value of the dependent property is NOT null, an empty string, empty array, or empty function.

Example

let Hamster = Ember.Object.extend({
  hasStuff: Ember.computed.notEmpty('backpack')
});

let hamster = Hamster.create({ backpack: ['Food', 'Sleeping Bag', 'Tent'] });

hamster.get('hasStuff');         // true
hamster.get('backpack').clear(); // []
hamster.get('hasStuff');         // false

Where computed.alias aliases get and set, and allows for bidirectional data flow, computed.oneWay only provides an aliased get. The set will not mutate the upstream property, rather causes the current property to become the value set. This causes the downstream property to permanently diverge from the upstream property.

Example

let User = Ember.Object.extend({
  firstName: null,
  lastName: null,
  nickName: Ember.computed.oneWay('firstName')
});

let teddy = User.create({
  firstName: 'Teddy',
  lastName:  'Zeenny'
});

teddy.get('nickName');              // 'Teddy'
teddy.set('nickName', 'TeddyBear'); // 'TeddyBear'
teddy.get('firstName');             // 'Teddy'

A computed property which performs a logical or on the original values for the provided dependent properties.

You may pass in more than two properties and even use property brace expansion. The computed property will return the first truthy value or last falsy value just like JavaScript's || operator.

Example

let Hamster = Ember.Object.extend({
  readyForRain: Ember.computed.or('hasJacket', 'hasUmbrella'),
  readyForBeach: Ember.computed.or('{hasSunscreen,hasUmbrella}')
});

let tomster = Hamster.create();

tomster.get('readyForRain'); // undefined
tomster.set('hasUmbrella', true);
tomster.get('readyForRain'); // true
tomster.set('hasJacket', 'Yes');
tomster.get('readyForRain'); // 'Yes'
tomster.set('hasSunscreen', 'Check');
tomster.get('readyForBeach'); // 'Check'

Where computed.oneWay provides oneWay bindings, computed.readOnly provides a readOnly one way binding. Very often when using computed.oneWay one does not also want changes to propagate back up, as they will replace the value.

This prevents the reverse flow, and also throws an exception when it occurs.

Example

let User = Ember.Object.extend({
  firstName: null,
  lastName: null,
  nickName: Ember.computed.readOnly('firstName')
});

let teddy = User.create({
  firstName: 'Teddy',
  lastName:  'Zeenny'
});

teddy.get('nickName');              // 'Teddy'
teddy.set('nickName', 'TeddyBear'); // throws Exception
// throw new Ember.Error('Cannot Set: nickName on: <User:ember27288>' );`
teddy.get('firstName');             // 'Teddy'

This is a more semantically meaningful alias of computed.oneWay, whose name is somewhat ambiguous as to which direction the data flows.

A computed property which returns a new array with all the properties from the first dependent array that are not in the second dependent array.

Example

let Hamster = Ember.Object.extend({
  likes: ['banana', 'grape', 'kale'],
  wants: Ember.computed.setDiff('likes', 'fruits')
});

let hamster = Hamster.create({
  fruits: [
    'grape',
    'kale',
  ]
});

hamster.get('wants'); // ['banana']

A computed property which returns a new array with all the properties from the first dependent array sorted based on a property or sort function.

The callback method you provide should have the following signature:

function(itemA, itemB);

• itemA the first item to compare.
• itemB the second item to compare.

This function should return negative number (e.g. -1) when itemA should come before itemB. It should return positive number (e.g. 1) when itemA should come after itemB. If the itemA and itemB are equal this function should return 0.

Therefore, if this function is comparing some numeric values, simple itemA - itemB or itemA.get( 'foo' ) - itemB.get( 'foo' ) can be used instead of series of if.

Example

let ToDoList = Ember.Object.extend({
  // using standard ascending sort
  todosSorting: ['name'],
  sortedTodos: Ember.computed.sort('todos', 'todosSorting'),

  // using descending sort
  todosSortingDesc: ['name:desc'],
  sortedTodosDesc: Ember.computed.sort('todos', 'todosSortingDesc'),

  // using a custom sort function
  priorityTodos: Ember.computed.sort('todos', function(a, b){
    if (a.priority > b.priority) {
      return 1;
    } else if (a.priority < b.priority) {
      return -1;
    }

    return 0;
  })
});

let todoList = ToDoList.create({todos: [
  { name: 'Unit Test', priority: 2 },
  { name: 'Documentation', priority: 3 },
  { name: 'Release', priority: 1 }
]});

todoList.get('sortedTodos');      // [{ name:'Documentation', priority:3 }, { name:'Release', priority:1 }, { name:'Unit Test', priority:2 }]
todoList.get('sortedTodosDesc');  // [{ name:'Unit Test', priority:2 }, { name:'Release', priority:1 }, { name:'Documentation', priority:3 }]
todoList.get('priorityTodos');    // [{ name:'Release', priority:1 }, { name:'Unit Test', priority:2 }, { name:'Documentation', priority:3 }]

A computed property that returns the sum of the values in the dependent array.

Alias for Ember.computed.uniq.

A computed property which returns a new array with all the unique elements from one or more dependent arrays.

Example

let Hamster = Ember.Object.extend({
  uniqueFruits: Ember.computed.uniq('fruits')
});

let hamster = Hamster.create({
  fruits: [
    'banana',
    'grape',
    'kale',
    'banana'
  ]
});

hamster.get('uniqueFruits'); // ['banana', 'grape', 'kale']

A computed property which returns a new array with all the unique elements from an array, with uniqueness determined by specific key.

Example

let Hamster = Ember.Object.extend({
  uniqueFruits: Ember.computed.uniqBy('fruits', 'id')
});
let hamster = Hamster.create({
  fruits: [
    { id: 1, 'banana' },
    { id: 2, 'grape' },
    { id: 3, 'peach' },
    { id: 1, 'banana' }
  ]
});
hamster.get('uniqueFruits'); // [ { id: 1, 'banana' }, { id: 2, 'grape' }, { id: 3, 'peach' }]