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.

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 @ContentChild?

ContentChildren is a parameter decorator that is used to fetch the QueryList of elements or directives from the content DOM. The QueryList is updated whenever the child element/component is added or removed.

What is the difference between @output and ViewChild?

While Angular inputs/outputs should be used when sharing data to and from child components, ViewChild should be used when trying to utilize properties and methods of the child component directly in the parent component.

What is ViewChild?

A ViewChild is a component, directive, or element as a part of a template. If we want to access a child component, directive, DOM element inside the parent component, we use the decorator @ViewChild() in Angular. … Since the child component can be located inside the parent component, it can accessed as @ViewChild.

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 use of @ViewChild?

The @ViewChild decorator allows us to inject into a component class references to elements used inside its template, that’s what we should use it for. Using @ViewChild we can easily inject components, directives or plain DOM elements.

What is @input in Angular?

A common pattern in Angular is sharing data between a parent component and one or more child components. … @Input() lets a parent component update data in the child component.

What are @input and @output in Angular?

@Input() and @Output() allow Angular to share data between the parent context and child directives or components. An @Input() property is writable while an @Output() property is observable.

What are the services in Angular?

Service is a broad category encompassing any value, function, or feature that an application needs. A service is typically a class with a narrow, well-defined purpose. It should do something specific and do it well. Angular distinguishes components from services to increase modularity and reusability.

Article first time published on

What is ViewChild and ContentChild?

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

How do I use ContentChild?

To use ContentChild , we need to import it first from the @angular/core . import { Component, ContentChild, ContentChildren, ElementRef, Renderer2, ViewChild } from ‘@angular/core’; Then use it to query the header from the projected content.

What is the difference between Ng-content ng container and ng-template?

To sum up, ng-content is used to display children in a template, ng-container is used as a non-rendered container to avoid having to add a span or a div, and ng-template allows you to group some content that is not rendered directly but can be used in other places of your template or you code.

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 used for in angular?

The ViewChild decorator is used to gain access to a child component, found in the template, so that you can access its properties and methods.

How can I get value from ViewChild?

1. // in html.
2. <input #input type=”text”>
3. // in .ts.
4. @ViewChild(‘input’) input:ElementRef;
5. //Output value.
6. console. log(this. input. nativeElement. value);

What is static in ViewChild?

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.

Why is ViewChild undefined?

Sometimes, if the component isn’t yet initialized when you access it, you get an error that says that the child component is undefined. … However, even if you access to the child component in the AfterViewInit, sometimes the @ViewChild was still returning null. The problem can be caused by the *ngIf or other directive.

What is view in angular?

Views are almost like their own virtual DOM. Each view contains a reference to a corresponding section of the DOM. Inside a view are nodes that mirror what is in the this section. Angular assigns one view node per DOM element. Each node holds a reference to a matching element.

What is child component in Angular?

An Angular application can contain thousands of components, and managing data communication may be complex. … In Angular, we can have a child component of a parent component where the child component has its own business logic and design that can act as a small unit of functionality for the whole component.

What is nativeElement in Angular?

Angular ElementRef is a wrapper around a native element inside of a View. It’s simply a class that wraps native DOM elements in the browser and allows you to work with the DOM by providing the nativeElement object which exposes all the methods and properties of the native elements.

What is projection in Angular?

Content projection is a pattern in which you insert, or project, the content you want to use inside another component. For example, you could have a Card component that accepts content provided by another component.

What is input output and EventEmitter in Angular?

@Input defines the input property in the component, which the parent component can set. … The @output defines the output property (event), which we raise in the child component using the EventEmitter . The parent listens to these events.

How does output work in Angular?

@Output decorator binds a property of a component, to send data from one component to the calling component. @Output binds a property of the type of angular EventEmitter class. To transfer the data from child to parent component, we use @Output decorator.

What is emitter in Angular?

Extends RxJS Subject for Angular by adding the emit() method. In the following example, a component defines two output properties that create event emitters. When the title is clicked, the emitter emits an open or close event to toggle the current visibility state.

What is lazy loading Angular?

Lazy loading is a technology of angular that allows you to load JavaScript components when a specific route is activated. It improves application load time speed by splitting the application into many bundles. When the user navigates by the app, bundles are loaded as needed.

What is injectable in Angular?

The @Injectable() decorator specifies that Angular can use this class in the DI system. The metadata, providedIn: ‘root’ , means that the HeroService is visible throughout the application. … If you define the component before the service, Angular returns a run-time null reference error.

What is two way data binding in Angular?

The two-way data binding in Angular enables data to flow from the component to the view and the other way round. It is used to display information to the end-user and allows them to make changes to the underlying data using the UI.

What is interceptor in Angular?

Interceptors are a unique type of Angular Service that we can implement. Interceptors allow us to intercept incoming or outgoing HTTP requests using the HttpClient . By intercepting the HTTP request, we can modify or change the value of the request. … HTTP Response Formatting. HTTP Error Handling.

What is singleton object in Angular?

A singleton is a class that allows only a single instance of itself to be created and gives access to that created instance. It contains static variables that can accommodate unique and private instances of itself. It is used in scenarios when a user wants to restrict instantiation of a class to only one object.

What is API in Angular?

API (Application Programming Interface) in AngularJS is a set of global JavaScript functions used for the purpose of carrying out the common tasks such as comparing objects, iterating objects, converting data. Some API functions in AngularJS are as follows : Comparing objects. Iterating objects.