$rootScope.Scope.$watchCollection()

$watchCollection(obj, listener);

Shallow watches the properties of an object and fires whenever any of the properties change (for arrays, this implies watching the array items; for object maps, this implies watching the properties). If a change is detected, the listener callback is fired.

The obj collection is observed via standard $watch operation and is examined on every call to $digest() to see if any items have been added, removed, or moved.
The listener is called whenever anything within the obj has changed. Examples include adding, removing, and moving items belonging to an object or array.

$scope.names = ['igor', 'matias', 'misko', 'james'];
$scope.dataCount = 4;
 
$scope.$watchCollection('names', function(newNames, oldNames) {
  $scope.dataCount = newNames.length;
});
 
expect($scope.dataCount).toEqual(4);
$scope.$digest();
 
//still at 4 ... no changes
expect($scope.dataCount).toEqual(4);
 
$scope.names.pop();
$scope.$digest();
 
//now there's been a change
expect($scope.dataCount).toEqual(3);

Parameters

Param Type Details

obj

Param	Type	Details
obj	`stringfunction(scope)`	Evaluated as expression. The expression value should evaluate to an object or an array which is observed on each $digest cycle. Any shallow change within the collection will trigger a call to the `listener`.
listener	`function(newCollection, oldCollection, scope)`	a callback function called when a change is detected. The `newCollection` object is the newly modified data obtained from the `obj` expression The `oldCollection` object is a copy of the former collection data. Due to performance considerations, the`oldCollection` value is computed only if the `listener` function declares two or more arguments. The `scope` argument refers to the current scope.

stringfunction(scope)

Evaluated as expression. The expression value should evaluate to an object or an array which is observed on each $digest cycle. Any shallow change within the collection will trigger a call to the listener.

listener

function(newCollection, oldCollection, scope)

a callback function called when a change is detected.

The newCollection object is the newly modified data obtained from the obj expression
The oldCollection object is a copy of the former collection data. Due to performance considerations, theoldCollection value is computed only if the listener function declares two or more arguments.
The scope argument refers to the current scope.

Returns

function()

Returns a de-registration function for this listener. When the de-registration function is executed, the internal watch operation is terminated.

Links:

https://docs.angularjs.org/api/ng/type/$rootScope.Scope#$watchCollection

doc_AngularJS

2025-01-10 15:47:30

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