What Are decorators?
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The Decorators are functions that modify
JavaScript classes and it also used for attaching metadata to classes.
Directive decorator and metadata Properties -
@Directive({
selector?: string
inputs?: string[]
outputs?: string[]
host?: {...}
providers?: Provider[]
exportAs?: string
queries?: {...}
})
Selector
–
It is a CSS selector that tells Angular to create an instance of this component
wherever it finds the corresponding tag in template HTML.
For example,
it is – <app-login></app-login>
CSS selector also triggers the instantiation of a
directive.
The selector may be declared by element name,
class name, attribute name, and attribute name & value.
Suppose we have a directive with an <input type="checkbox">
selector and the HTML looks like this.
<form>
<label>Name
-</label>
<input
type="text">
<label>Are
you agree? </label>
<input
type="checkbox">
<form>
The directive will only be instantiated on the <input type="checkbox">
element.
Inputs–
The list of class property names to data-bind as component inputs
Outputs
-
The list of class property names that expose output events that others can
subscribe too
Host–
These properties use to map the class property to host element bindings for properties,
events, actions, and attributes.
The host looks like this.
@Directive({
selector: 'button',
host: {'(click)':
'onClick($event.target)'}
})
Providers
-
list of providers available to this component and its children
Queries–
To configure queries that can be injected into the component
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