angular-docs-cn/packages/core/src/render3/metadata.ts

/**
 * @license
 * Copyright Google Inc. 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 {Type} from '../interface/type';
import {noSideEffects} from '../util/closure';

interface TypeWithMetadata extends Type<any> {
  decorators?: any[];
  ctorParameters?: () => any[];
  propDecorators?: {[field: string]: any};
}

/**
 * Adds decorator, constructor, and property metadata to a given type via static metadata fields
 * on the type.
 *
 * These metadata fields can later be read with Angular's `ReflectionCapabilities` API.
 *
 * Calls to `setClassMetadata` can be marked as pure, resulting in the metadata assignments being
 * tree-shaken away during production builds.
 */
export function setClassMetadata(
    type: Type<any>, decorators: any[]|null, ctorParameters: (() => any[])|null,
    propDecorators: {[field: string]: any}|null): void {
  return noSideEffects(() => {
           const clazz = type as TypeWithMetadata;

           // We determine whether a class has its own metadata by taking the metadata from the
           // parent constructor and checking whether it's the same as the subclass metadata below.
           // We can't use `hasOwnProperty` here because it doesn't work correctly in IE10 for
           // static fields that are defined by TS. See
           // https://github.com/angular/angular/pull/28439#issuecomment-459349218.
           const parentPrototype = clazz.prototype ? Object.getPrototypeOf(clazz.prototype) : null;
           const parentConstructor: TypeWithMetadata|null =
               parentPrototype && parentPrototype.constructor;

           if (decorators !== null) {
             if (clazz.decorators !== undefined &&
                 (!parentConstructor || parentConstructor.decorators !== clazz.decorators)) {
               clazz.decorators.push(...decorators);
             } else {
               clazz.decorators = decorators;
             }
           }
           if (ctorParameters !== null) {
             // Rather than merging, clobber the existing parameters. If other projects exist which
             // use tsickle-style annotations and reflect over them in the same way, this could
             // cause issues, but that is vanishingly unlikely.
             clazz.ctorParameters = ctorParameters;
           }
           if (propDecorators !== null) {
             // The property decorator objects are merged as it is possible different fields have
             // different decorator types. Decorators on individual fields are not merged, as it's
             // also incredibly unlikely that a field will be decorated both with an Angular
             // decorator and a non-Angular decorator that's also been downleveled.
             if (clazz.propDecorators !== undefined &&
                 (!parentConstructor ||
                  parentConstructor.propDecorators !== clazz.propDecorators)) {
               clazz.propDecorators = {...clazz.propDecorators, ...propDecorators};
             } else {
               clazz.propDecorators = propDecorators;
             }
           }
         }) as never;
}