@angular/core
Version:
Angular - the core framework
79 lines • 7.38 kB
JavaScript
/**
* @license
* Copyright Google LLC All Rights Reserved.
*
* Use of this source code is governed by an MIT-style license that can be
* found in the LICENSE file at https://angular.io/license
*/
import { getClosureSafeProperty } from '../util/property';
import { stringify } from '../util/stringify';
const __forward_ref__ = getClosureSafeProperty({ __forward_ref__: getClosureSafeProperty });
/**
* Allows to refer to references which are not yet defined.
*
* For instance, `forwardRef` is used when the `token` which we need to refer to for the purposes of
* DI is declared, but not yet defined. It is also used when the `token` which we use when creating
* a query is not yet defined.
*
* `forwardRef` is also used to break circularities in standalone components imports.
*
* @usageNotes
* ### Circular dependency example
* {@example core/di/ts/forward_ref/forward_ref_spec.ts region='forward_ref'}
*
* ### Circular standalone reference import example
* ```ts
* @Component({
* standalone: true,
* imports: [ChildComponent],
* selector: 'app-parent',
* template: `<app-child [hideParent]="hideParent"></app-child>`,
* })
* export class ParentComponent {
* @Input() hideParent: boolean;
* }
*
*
* @Component({
* standalone: true,
* imports: [CommonModule, forwardRef(() => ParentComponent)],
* selector: 'app-child',
* template: `<app-parent *ngIf="!hideParent"></app-parent>`,
* })
* export class ChildComponent {
* @Input() hideParent: boolean;
* }
* ```
*
* @publicApi
*/
export function forwardRef(forwardRefFn) {
forwardRefFn.__forward_ref__ = forwardRef;
forwardRefFn.toString = function () {
return stringify(this());
};
return forwardRefFn;
}
/**
* Lazily retrieves the reference value from a forwardRef.
*
* Acts as the identity function when given a non-forward-ref value.
*
* @usageNotes
* ### Example
*
* {@example core/di/ts/forward_ref/forward_ref_spec.ts region='resolve_forward_ref'}
*
* @see {@link forwardRef}
* @publicApi
*/
export function resolveForwardRef(type) {
return isForwardRef(type) ? type() : type;
}
/** Checks whether a function is wrapped by a `forwardRef`. */
export function isForwardRef(fn) {
return (typeof fn === 'function' &&
fn.hasOwnProperty(__forward_ref__) &&
fn.__forward_ref__ === forwardRef);
}
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ApO1xufVxuIl19