Angular

In this article, we will learn how to implement Cross Field validation or mult field Validation in Angular. We learned how to validate reactive forms & how to create a custom validator. Those articles showed how to validate a Single Form Control. But some times we also come across fields whose value depends on another field. For example, the following scenario’s requires us to compare two fields.

n this guide let us learn how to create a custom async validator in Angular. The creating an async validator is very similar to the Sync validators. The only difference is that the async Validators must return the result of the validation as an observable (or as Promise).

The ViewChild or ViewChildren decorators are used to Query and get the reference of the DOM element injected inside an Angular component. ViewChild returns the first matching element and ViewChildren returns all the matching elements as a QueryList of items. We can use these references to manipulate element properties in the component. To Query a DOM element(s), we must supply the query selector, which can be a string or a type as the first argument to the ViewChild or ViewChildren. The argument static determines whether the query is performed, before or after the change detection. The read option allows us to query a different token rather than the default and is useful when the element is associated with multiple types. We will learn all these in this tutorial.

The HostBinding & HostListener are decorators in Angular. HostListener listens to host events, while HostBinding allows us to bind to a property of the host element. The host is an element on which we attach our component or directive. This feature allows us to manipulate the host styles or take some action whenever the user performs some action on the host element.