How directives are compiled?

How directives are compiled?

For a single directive We can see that compile is executed first, then controller , then pre-link and last is post-link .

What is $compile in AngularJS?

Compiles an HTML string or DOM into a template and produces a template function, which can then be used to link scope and the template together. The compilation is a process of walking the DOM tree and matching DOM elements to directives.

What is the difference between controller and link in directives?

Answer:The link option is just a shortcut to setting up a post-link function. controller: The directive controller can be passed to another directive linking/compiling phase. It can be injected into other directices as a mean to use in inter-directive communication.

What is directive definition object DDO?

The Directive Definition Object (DDO) tells the compiler how a Directive needs to be assembled. Common properties include the link function, controller function, restrict, template, and templateUrl.

What is the default value for priority property in Directive definition?

priority. Specify the order in which directives are applied to the DOM. Directives are compiled in priority order, from highest to lowest. The default is 0.

What is $scope AngularJS?

The $scope in an AngularJS is a built-in object, which contains application data and methods. You can create properties to a $scope object inside a controller function and assign a value or function to it. The $scope is glue between a controller and view (HTML).

Is Angular JS in demand?

Angular JS is a JavaScript based front-end web development platform commonly used in the modern interactive web applications in the marketplace. The demand of Angular JS developers is consistently increasing the every enhanced version of this platform.

What is difference between $scope and scope?

In Angular js $scope is used whenever we have to use dependency injection (D.I) whereas as the scope is used for directive linking.

How many types of directives are there?

four types

What is the difference between ViewChild () and ContentChild ()?

ViewChild is used to select an element from component’s template while ContentChild is used to select projected content.

Why do we use ViewChild?

The viewchild can get be used to get reference of template elements, so you can see all the associated attributes. A common example would be if there were to be a custom component in a template a ViewChild could be used to pull values out of that component when needed.

What is ViewChild static?

The static option for @ViewChild() and @ContentChild() queries determines when the query results become available. With static queries (static: true), the query resolves once the view has been created, but before change detection runs.

What is the difference between ViewChild and ViewChildren?

Another critical difference is that @ViewChild returns a single native DOM element as a reference, while the @ViewChildren decorator returns the list of different native DOM elements in the form of QueryList , which contains the set of elements.

What is read in ViewChild?

With {read: SomeType} you tell what type should be returned from the element with the #myname template variable. If you don’t provide the read parameter, @ViewChild() returns the. ElementRef instance if there is no component applied, or the. component instance if there is.

What is ViewChild decorator in angular?

ViewChildlink Property decorator that configures a view query. The change detector looks for the first element or the directive matching the selector in the view DOM. If the view DOM changes, and a new child matches the selector, the property is updated.

What is @input in angular?

A common pattern in Angular is sharing data between a parent component and one or more child components. @Input() allows a parent component to update data in the child component. Conversely, @Output() allows the child to send data to a parent component.

What is AfterViewInit in angular?

AfterViewInitlink A lifecycle hook that is called after Angular has fully initialized a component’s view. Define an ngAfterViewInit() method to handle any additional initialization tasks.

What is TemplateRef in angular?

TemplateReflink Represents an embedded template that can be used to instantiate embedded views. To instantiate embedded views based on a template, use the ViewContainerRef method createEmbeddedView() .

What is difference between ngOnInit and constructor?

The main difference between constructor and ngOnInit is that ngOnInit is lifecycle hook and runs after constructor. Component interpolated template and input initial values aren’t available in constructor, but they are available in ngOnInit . The practical difference is how ngOnInit affects how the code is structured.

What is ngOnChanges in angular?

As the Angular core docs clearly states, the ngOnChanges() method is a lifecycle hook that will trigger each time Angular sets a data-bound input property. That means that it should be used whenever we need something to happen whenever that property value changes.

What triggers ngOnChanges?

ngOnChanges triggers following the modification of @Input bound class members. Data bound by the @Input() decorator come from an external source. When the external source alters that data in a detectable manner, it passes through the @Input property again. With this update, ngOnChanges immediately fires.

What is difference between ngOnChanges and ngDoCheck?

ngOnChanges() ( OnChanges ) is called when a value bound to an input has changed so you can run custom code when an input has changed. ngDoCheck() ( DoCheck ) is called when change detection runs so you can implement your custom change detection action.

What is the difference between ngOnInit and ngOnChanges?

ngOnInit() is used to execute any piece of code for only one time (for eg : data fetch on load). ngOnChanges() will execute on every @Input() property change. If you want to execute any component method, based on the @Input() value change, then you should write such logic inside ngOnChanges() .

How observables are used?

Angular makes use of observables as an interface to handle a variety of common asynchronous operations. You can define custom events that send observable output data from a child to a parent component. The HTTP module uses observables to handle AJAX requests and responses.

Why are ngOnChanges used?

ngOnChanges respond when data-bound input properties changes. The method receives a SimpleChanges object of current and previous property values. ngOnChanges methods come in OnChanges interface. This can be used when we are using two-way data binding.

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