A root scope can be retrieved using the $rootScope key from the $injector. Child scopes are created using the $new() method. (Most scopes are created automatically when compiled HTML template is executed.)
Here is a simple scope snippet to show how you can interact with the scope.
<file src="./test/ng/rootScopeSpec.js" tag="docs1" />
A scope can inherit from a parent scope, as in this example:
var parent = $rootScope; var child = parent.$new(); parent.salutation = "Hello"; child.name = "World"; expect(child.salutation).toEqual('Hello'); child.salutation = "Welcome"; expect(child.salutation).toEqual('Welcome'); expect(parent.salutation).toEqual('Hello');
$rootScope.Scope([providers], [instanceCache]);
Param | Type | Details |
---|---|---|
providers (optional) | Object.<string, function()>= | Map of service factory which need to be provided for the current scope. Defaults to |
instanceCache (optional) | Object.<string, *>= | Provides pre-instantiated services which should append/override services provided by |
Object |
Newly created scope. |
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.
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. |
Object |
The newly created child scope. |
Registers a listener
callback to be executed whenever the watchExpression
changes.
watchExpression
is called on every call to $digest() and should return the value that will be watched. (Since $digest() reruns when it detects changes the watchExpression
can execute multiple times per $digest() and should be idempotent.)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)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.listener
may change the model, which may trigger other listener
s 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
. (Since watchExpression
can execute multiple times per $digest cycle when a change is detected, be prepared for multiple calls to your listener.)
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.
The example below contains an illustration of using a function as your $watch listener
// 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.$digest(); expect(scope.counter).toEqual(2); // Using a listener function var food; scope.foodCounter = 0; expect(scope.foodCounter).toEqual(0); scope.$watch( // This is the listener function function() { return food; }, // This is the change handler 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);
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 (optional) | function() string | Callback called whenever the return value of the
|
objectEquality (optional) | boolean | Compare for object equality using |
function() |
Returns a deregistration function for this 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.
obj
collection is observed via standard $watch operation and is examined on every call to $digest() to see if any items have been added, removed, or moved.listener
is called whenever anything within the obj
has changed. Examples include adding, removing, and moving items belonging to an object or array.$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);
Param | Type | Details |
---|---|---|
obj | string function(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 | function(newCollection, oldCollection, scope) | a callback function called when a change is detected.
|
function() |
Returns a de-registration function for this listener. When the de-registration function is executed, the internal watch operation is terminated. |
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 directives), 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);
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 $destroy
jQuery event, which can be used to clean up DOM bindings before an element is removed from the DOM.
Executes the expression
on the current scope and returns the result. Any exceptions in the expression are propagated (uncaught). This is useful when evaluating Angular expressions.
var scope = ng.$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);
Param | Type | Details |
---|---|---|
expression (optional) | string function() | An angular expression to be executed.
|
locals (optional) | object | Local variables object, useful for overriding values in scope. |
* |
The result of evaluating the expression. |
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:
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
.
Param | Type | Details |
---|---|---|
expression (optional) | string function() | An angular expression to be executed.
|
$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.
function $apply(expr) { try { return $eval(expr); } catch (e) { $exceptionHandler(e); } finally { $root.$digest(); } }
Scope's $apply()
method transitions through the following stages:
Param | Type | Details |
---|---|---|
exp (optional) | string function() | An angular expression to be executed.
|
* |
The result of evaluating the expression. |
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 current scope which is handling the event.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.Param | Type | Details |
---|---|---|
name | string | Event name to listen on. |
listener | function(event, ...args) | Function to call when the event is emitted. |
function() |
Returns a deregistration function for this listener. |
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.
Param | Type | Details |
---|---|---|
name | string | Event name to emit. |
args | * | Optional one or more arguments which will be passed onto the event listeners. |
Object |
Event object (see |
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.
Param | Type | Details |
---|---|---|
name | string | Event name to broadcast. |
args | * | Optional one or more arguments which will be passed onto the event listeners. |
Object |
Event object, see |
Broadcasted when a scope and its children are being destroyed.
Note that, in AngularJS, there is also a $destroy
jQuery event, which can be used to clean up DOM bindings before an element is removed from the DOM.
Unique scope ID (monotonically increasing) useful for debugging. |
Reference to the parent scope. |
Reference to the root scope. |
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Licensed under the Creative Commons Attribution License 4.0.
https://code.angularjs.org/1.2.32/docs/api/ng/type/$rootScope.Scope