This mixin implements Observer-friendly Array-like behavior. It is not a concrete implementation, but it can be used up by other classes that want to appear like arrays.

For example, ArrayProxy is a concrete classes that can be instantiated to implement array-like behavior. Both of these classes use the Array Mixin by way of the MutableArray mixin, which allows observable changes to be made to the underlying array.

Unlike Ember.Enumerable, this mixin defines methods specifically for collections that provide index-ordered access to their contents. When you are designing code that needs to accept any kind of Array-like object, you should use these methods instead of Array primitives because these will properly notify observers of changes to the array.

Although these methods are efficient, they do add a layer of indirection to your application so it is a good idea to use them only when you need the flexibility of using both true JavaScript arrays and "virtual" arrays such as controllers and collections.

You can use the methods defined in this module to access and modify array contents in a KVO-friendly way. You can also be notified whenever the membership of an array changes by using .observes('myArray.[]').

To support Ember.Array in your own class, you must override two primitives to use it: length() and objectAt().

Note that the Ember.Array mixin also incorporates the Ember.Enumerable mixin. All Ember.Array-like objects are also enumerable.

Adds an array observer to the receiving array. The array observer object normally must implement two methods:

• arrayWillChange(observedObj, start, removeCount, addCount) - This method will be called just before the array is modified.
• arrayDidChange(observedObj, start, removeCount, addCount) - This method will be called just after the array is modified.

Both callbacks will be passed the observed object, starting index of the change as well as a count of the items to be removed and added. You can use these callbacks to optionally inspect the array during the change, clear caches, or do any other bookkeeping necessary.

In addition to passing a target, you can also include an options hash which you can use to override the method names that will be invoked on the target.

If you are implementing an object that supports Ember.Array, call this method just after the array content changes to notify any observers and invalidate any related properties. Pass the starting index of the change as well as a delta of the amounts to change.

If you are implementing an object that supports Ember.Array, call this method just before the array content changes to notify any observers and invalidate any related properties. Pass the starting index of the change as well as a delta of the amounts to change.

Returns true if the passed object can be found in the array. This method is a Polyfill for ES 2016 Array.includes. If no startAt argument is given, the starting location to search is 0. If it's negative, searches from the index of this.length + startAt by asc.

[1, 2, 3].includes(2);     // true
[1, 2, 3].includes(4);     // false
[1, 2, 3].includes(3, 2);  // true
[1, 2, 3].includes(3, 3);  // false
[1, 2, 3].includes(3, -1); // true
[1, 2, 3].includes(1, -1); // false
[1, 2, 3].includes(1, -4); // true
[1, 2, NaN].includes(NaN); // true

Returns the index of the given object's first occurrence. If no startAt argument is given, the starting location to search is 0. If it's negative, will count backward from the end of the array. Returns -1 if no match is found.

let arr = ['a', 'b', 'c', 'd', 'a'];

arr.indexOf('a');       //  0
arr.indexOf('z');       // -1
arr.indexOf('a', 2);    //  4
arr.indexOf('a', -1);   //  4
arr.indexOf('b', 3);    // -1
arr.indexOf('a', 100);  // -1

Returns the index of the given object's last occurrence. If no startAt argument is given, the search starts from the last position. If it's negative, will count backward from the end of the array. Returns -1 if no match is found.

let arr = ['a', 'b', 'c', 'd', 'a'];

arr.lastIndexOf('a');       //  4
arr.lastIndexOf('z');       // -1
arr.lastIndexOf('a', 2);    //  0
arr.lastIndexOf('a', -1);   //  4
arr.lastIndexOf('b', 3);    //  1
arr.lastIndexOf('a', 100);  //  4

Returns the object at the given index. If the given index is negative or is greater or equal than the array length, returns undefined.

This is one of the primitives you must implement to support Ember.Array. If your object supports retrieving the value of an array item using get() (i.e. myArray.get(0)), then you do not need to implement this method yourself.

let arr = ['a', 'b', 'c', 'd'];

arr.objectAt(0);   // 'a'
arr.objectAt(3);   // 'd'
arr.objectAt(-1);  // undefined
arr.objectAt(4);   // undefined
arr.objectAt(5);   // undefined

This returns the objects at the specified indexes, using objectAt.

let arr = ['a', 'b', 'c', 'd'];

arr.objectsAt([0, 1, 2]);  // ['a', 'b', 'c']
arr.objectsAt([2, 3, 4]);  // ['c', 'd', undefined]

Removes an array observer from the object if the observer is current registered. Calling this method multiple times with the same object will have no effect.

Returns a new array that is a slice of the receiver. This implementation uses the observable array methods to retrieve the objects for the new slice.

let arr = ['red', 'green', 'blue'];

arr.slice(0);       // ['red', 'green', 'blue']
arr.slice(0, 2);    // ['red', 'green']
arr.slice(1, 100);  // ['green', 'blue']

Returns a special object that can be used to observe individual properties on the array. Just get an equivalent property on this object and it will return an enumerable that maps automatically to the named key on the member objects.

@each should only be used in a non-terminal context. Example:

myMethod: computed('[email protected]', function(){
  ...
});

If you merely want to watch for the array being changed, like an object being replaced, added or removed, use [] instead of @each.

myMethod: computed('posts.[]', function(){
  ...
});

This is the handler for the special array content property. If you get this property, it will return this. If you set this property to a new array, it will replace the current content.

This property overrides the default property defined in Ember.Enumerable.

Becomes true whenever the array currently has observers watching changes on the array.

Required. You must implement this method to apply this mixin.

Your array must support the length property. Your replace methods should set this property whenever it changes.