angular2
Version:
Angular 2 - a web framework for modern web apps
59 lines • 1.83 kB
JavaScript
import { stringify, isFunction } from 'angular2/src/facade/lang';
/**
* 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.
*
* ### Example ([live demo](http://plnkr.co/edit/bRs0SX2OTQiJzqvjgl8P?p=preview))
*
* ```typescript
* class Door {
* lock: Lock;
* constructor(@Inject(forwardRef(() => Lock)) lock:Lock) {
* this.lock = lock;
* }
* }
*
* // Only at this point Lock is defined.
* class Lock {
* }
*
* var injector = Injector.resolveAndCreate([Door, Lock]);
* var door = injector.get(Door);
* expect(door instanceof Door).toBe(true);
* expect(door.lock instanceof Lock).toBe(true);
* ```
*/
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.
*
* ### Example ([live demo](http://plnkr.co/edit/GU72mJrk1fiodChcmiDR?p=preview))
*
* ```typescript
* var ref = forwardRef(() => "refValue");
* expect(resolveForwardRef(ref)).toEqual("refValue");
* expect(resolveForwardRef("regularValue")).toEqual("regularValue");
* ```
*
* See: {@link forwardRef}
*/
export function resolveForwardRef(type) {
if (isFunction(type) && type.hasOwnProperty('__forward_ref__') &&
type.__forward_ref__ === forwardRef) {
return type();
}
else {
return type;
}
}
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