$rootScope.Scope

Usage

$rootScope.Scope([providers], [instanceCache]);

Arguments

Returns

Methods

• $new(isolate, parent);

  Creates a new child scope.

  The parent scope will propagate the $digest() event. The scope can be removed from the scope hierarchy using $destroy().

  $destroy() must be called on a scope when it is desired for the scope and its child scopes to be permanently detached from the parent and thus stop participating in model change detection and listener notification by invoking.

  Parameters

  Param	Type	Details
  isolate	boolean	If true, then the scope does not prototypically inherit from the parent scope. The scope is isolated, as it can not see parent scope properties. When creating widgets, it is useful for the widget to not accidentally read parent state.
  parent (optional)	Scope	The Scope that will be the $parent of the newly created scope. Defaults to this scope if not provided. This is used when creating a transclude scope to correctly place it in the scope hierarchy while maintaining the correct prototypical inheritance. (default: this)

  Returns

  Object

  The newly created child scope.

• $watch(watchExpression, listener, [objectEquality]);

  Registers a listener callback to be executed whenever the watchExpression changes.

  • The watchExpression is called on every call to $digest() and should return the value that will be watched. (watchExpression should not change its value when executed multiple times with the same input because it may be executed multiple times by $digest(). That is, watchExpression should be idempotent.
  • The listener is called only when the value from the current watchExpression and the previous call to watchExpression are not equal (with the exception of the initial run, see below). Inequality is determined according to reference inequality, strict comparison via the !== Javascript operator, unless objectEquality == true (see next point)
  • When objectEquality == true, inequality of the watchExpression is determined according to the angular.equals function. To save the value of the object for later comparison, the angular.copy function is used. This therefore means that watching complex objects will have adverse memory and performance implications.
  • The watch listener may change the model, which may trigger other listeners to fire. This is achieved by rerunning the watchers until no changes are detected. The rerun iteration limit is 10 to prevent an infinite loop deadlock.

  If you want to be notified whenever $digest is called, you can register a watchExpression function with no listener. (Be prepared for multiple calls to your watchExpression because it will execute multiple times in a single $digest cycle if a change is detected.)

  After a watcher is registered with the scope, the listener fn is called asynchronously (via $evalAsync) to initialize the watcher. In rare cases, this is undesirable because the listener is called when the result of watchExpression didn't change. To detect this scenario within the listener fn, you can compare the newVal and oldVal. If these two values are identical (===) then the listener was called due to initialization.

  // let's assume that scope was dependency injected as the $rootScope
  var scope = $rootScope;
  scope.name = 'misko';
  scope.counter = 0;
  
  expect(scope.counter).toEqual(0);
  scope.$watch('name', function(newValue, oldValue) {
    scope.counter = scope.counter + 1;
  });
  expect(scope.counter).toEqual(0);
  
  scope.$digest();
  // the listener is always called during the first $digest loop after it was registered
  expect(scope.counter).toEqual(1);
  
  scope.$digest();
  // but now it will not be called unless the value changes
  expect(scope.counter).toEqual(1);
  
  scope.name = 'adam';
  scope.$digest();
  expect(scope.counter).toEqual(2);
  
  
  
  // Using a function as a watchExpression
  var food;
  scope.foodCounter = 0;
  expect(scope.foodCounter).toEqual(0);
  scope.$watch(
    // This function returns the value being watched. It is called for each turn of the $digest loop
    function() { return food; },
    // This is the change listener, called when the value returned from the above function changes
    function(newValue, oldValue) {
      if ( newValue !== oldValue ) {
        // Only increment the counter if the value changed
        scope.foodCounter = scope.foodCounter + 1;
      }
    }
  );
  // No digest has been run so the counter will be zero
  expect(scope.foodCounter).toEqual(0);
  
  // Run the digest but since food has not changed count will still be zero
  scope.$digest();
  expect(scope.foodCounter).toEqual(0);
  
  // Update food and run digest.  Now the counter will increment
  food = 'cheeseburger';
  scope.$digest();
  expect(scope.foodCounter).toEqual(1);
  

  Parameters

  Param	Type	Details
  watchExpression	function()string	Expression that is evaluated on each $digest cycle. A change in the return value triggers a call to the listener. string: Evaluated as expression function(scope): called with current scope as a parameter.
  listener	function(newVal, oldVal, scope)	Callback called whenever the value of watchExpression changes. newVal contains the current value of the watchExpression oldVal contains the previous value of the watchExpression scope refers to the current scope
  objectEquality (optional)	boolean	Compare for object equality using angular.equals instead of comparing for reference equality. (default: false)

  Returns

  function()

  Returns a deregistration function for this listener.

• $watchGroup(watchExpressions, listener);

  A variant of $watch() where it watches an array of watchExpressions. If any one expression in the collection changes the listener is executed.

  • The items in the watchExpressions array are observed via standard $watch operation and are examined on every call to $digest() to see if any items changes.
  • The listener is called whenever any expression in the watchExpressions array changes.

  Parameters

  Param	Type	Details
  watchExpressions	Array.<string|Function(scope)>	Array of expressions that will be individually watched using $watch()
  listener	function(newValues, oldValues, scope)	Callback called whenever the return value of any expression in watchExpressions changes The newValues array contains the current values of the watchExpressions, with the indexes matching those of watchExpression and the oldValues array contains the previous values of the watchExpressions, with the indexes matching those of watchExpression The scope refers to the current scope.

  Returns

  function()

  Returns a de-registration function for all listeners.

• $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	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.

• $digest();

  Processes all of the watchers of the current scope and its children. Because a watcher's listener can change the model, the $digest() keeps calling the watchers until no more listeners are firing. This means that it is possible to get into an infinite loop. This function will throw 'Maximum iteration limit exceeded.' if the number of iterations exceeds 10.

  Usually, you don't call $digest() directly in controllers or in directives. Instead, you should call $apply() (typically from within a directive), which will force a $digest().

  If you want to be notified whenever $digest() is called, you can register a watchExpression function with $watch() with no listener.

  In unit tests, you may need to call $digest() to simulate the scope life cycle.

  var scope = ...;
  scope.name = 'misko';
  scope.counter = 0;
  
  expect(scope.counter).toEqual(0);
  scope.$watch('name', function(newValue, oldValue) {
    scope.counter = scope.counter + 1;
  });
  expect(scope.counter).toEqual(0);
  
  scope.$digest();
  // the listener is always called during the first $digest loop after it was registered
  expect(scope.counter).toEqual(1);
  
  scope.$digest();
  // but now it will not be called unless the value changes
  expect(scope.counter).toEqual(1);
  
  scope.name = 'adam';
  scope.$digest();
  expect(scope.counter).toEqual(2);
  

• $destroy();

  Removes the current scope (and all of its children) from the parent scope. Removal implies that calls to $digest() will no longer propagate to the current scope and its children. Removal also implies that the current scope is eligible for garbage collection.

  The $destroy() is usually used by directives such as ngRepeat for managing the unrolling of the loop.

  Just before a scope is destroyed, a $destroy event is broadcasted on this scope. Application code can register a $destroy event handler that will give it a chance to perform any necessary cleanup.

  Note that, in AngularJS, there is also a $destroy jQuery event, which can be used to clean up DOM bindings before an element is removed from the DOM.

• $eval([expression], [locals]);

  Executes the expression on the current scope and returns the result. Any exceptions in the expression are propagated (uncaught). This is useful when evaluating Angular expressions.

  var scope = ng.$rootScope.Scope();
  scope.a = 1;
  scope.b = 2;
  
  expect(scope.$eval('a+b')).toEqual(3);
  expect(scope.$eval(function(scope){ return scope.a + scope.b; })).toEqual(3);
  

  Parameters

  Param	Type	Details
  expression (optional)	stringfunction()	An angular expression to be executed. string: execute using the rules as defined in expression. function(scope): execute the function with the current scope parameter.
  locals (optional)	object	Local variables object, useful for overriding values in scope.

  Returns

  *	The result of evaluating the expression.

• $evalAsync([expression], [locals]);

  Executes the expression on the current scope at a later point in time.

  The $evalAsync makes no guarantees as to when the expression will be executed, only that:

  • it will execute after the function that scheduled the evaluation (preferably before DOM rendering).
  • at least one $digest cycle will be performed after expression execution.

  Any exceptions from the execution of the expression are forwarded to the $exceptionHandler service.

  Note: if this function is called outside of a $digest cycle, a new $digest cycle will be scheduled. However, it is encouraged to always call code that changes the model from within an $apply call. That includes code evaluated via $evalAsync.

  Parameters

  Param	Type	Details
  expression (optional)	stringfunction()	An angular expression to be executed. string: execute using the rules as defined in expression. function(scope): execute the function with the current scope parameter.
  locals (optional)	object	Local variables object, useful for overriding values in scope.

• $apply([exp]);

  $apply() is used to execute an expression in angular from outside of the angular framework. (For example from browser DOM events, setTimeout, XHR or third party libraries). Because we are calling into the angular framework we need to perform proper scope life cycle of exception handling, executing watches.

  Life cycle

  Pseudo-Code of $apply()

  function $apply(expr) {
    try {
      return $eval(expr);
    } catch (e) {
      $exceptionHandler(e);
    } finally {
      $root.$digest();
    }
  }
  

  Scope's $apply() method transitions through the following stages:

  1. The expression is executed using the $eval() method.
  2. Any exceptions from the execution of the expression are forwarded to the $exceptionHandler service.
  3. The watch listeners are fired immediately after the expression was executed using the $digest() method.

  Parameters

  Param	Type	Details
  exp (optional)	stringfunction()	An angular expression to be executed. string: execute using the rules as defined in expression. function(scope): execute the function with current scope parameter.

  Returns

  *	The result of evaluating the expression.

• $applyAsync([exp]);

  Schedule the invocation of $apply to occur at a later time. The actual time difference varies across browsers, but is typically around ~10 milliseconds.

  This can be used to queue up multiple expressions which need to be evaluated in the same digest.

  Parameters

  Param	Type	Details
  exp (optional)	stringfunction()	An angular expression to be executed. string: execute using the rules as defined in expression. function(scope): execute the function with current scope parameter.

• $on(name, listener);

  Listens on events of a given type. See $emit for discussion of event life cycle.

  The event listener function format is: function(event, args...). The event object passed into the listener has the following attributes:

  • targetScope - {Scope}: the scope on which the event was $emit-ed or $broadcast-ed.
  • currentScope - {Scope}: the scope that is currently handling the event. Once the event propagates through the scope hierarchy, this property is set to null.
  • name - {string}: name of the event.
  • stopPropagation - {function=}: calling stopPropagation function will cancel further event propagation (available only for events that were $emit-ed).
  • preventDefault - {function}: calling preventDefault sets defaultPrevented flag to true.
  • defaultPrevented - {boolean}: true if preventDefault was called.

  Parameters

  Param	Type	Details
  name	string	Event name to listen on.
  listener	function(event, ...args)	Function to call when the event is emitted.

  Returns

  function()

  Returns a deregistration function for this listener.

• $emit(name, args);

  Dispatches an event name upwards through the scope hierarchy notifying the registered $rootScope.Scope listeners.

  The event life cycle starts at the scope on which $emit was called. All listeners listening for name event on this scope get notified. Afterwards, the event traverses upwards toward the root scope and calls all registered listeners along the way. The event will stop propagating if one of the listeners cancels it.

  Any exception emitted from the listeners will be passed onto the $exceptionHandler service.

  Parameters

  Param	Type	Details
  name	string	Event name to emit.
  args	*	Optional one or more arguments which will be passed onto the event listeners.

  Returns

  Object

  Event object (see $rootScope.Scope).

• $broadcast(name, args);

  Dispatches an event name downwards to all child scopes (and their children) notifying the registered $rootScope.Scope listeners.

  The event life cycle starts at the scope on which $broadcast was called. All listeners listening for name event on this scope get notified. Afterwards, the event propagates to all direct and indirect scopes of the current scope and calls all registered listeners along the way. The event cannot be canceled.

  Any exception emitted from the listeners will be passed onto the $exceptionHandler service.

  Parameters

  Param	Type	Details
  name	string	Event name to broadcast.
  args	*	Optional one or more arguments which will be passed onto the event listeners.

  Returns

  Object

  Event object, see $rootScope.Scope

Events

• $destroy

  Broadcasted when a scope and its children are being destroyed.

  Note that, in AngularJS, there is also a $destroy jQuery event, which can be used to clean up DOM bindings before an element is removed from the DOM.

  Type:

  broadcast

  Target:

  scope being destroyed

Properties

• $id

  Unique scope ID (monotonically increasing) useful for debugging.

• $parent

  Reference to the parent scope.

• $root

  Reference to the root scope.