| import { Operator } from '../Operator'; |
| import { Subscriber } from '../Subscriber'; |
| import { Observable } from '../Observable'; |
| import { OperatorFunction, MonoTypeOperatorFunction, TeardownLogic } from '../types'; |
| |
| /* tslint:disable:max-line-length */ |
| export function filter<T, S extends T>(predicate: (value: T, index: number) => value is S, |
| thisArg?: any): OperatorFunction<T, S>; |
| export function filter<T>(predicate: (value: T, index: number) => boolean, |
| thisArg?: any): MonoTypeOperatorFunction<T>; |
| /* tslint:enable:max-line-length */ |
| |
| /** |
| * Filter items emitted by the source Observable by only emitting those that |
| * satisfy a specified predicate. |
| * |
| * <span class="informal">Like |
| * [Array.prototype.filter()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter), |
| * it only emits a value from the source if it passes a criterion function.</span> |
| * |
| * ![](filter.png) |
| * |
| * Similar to the well-known `Array.prototype.filter` method, this operator |
| * takes values from the source Observable, passes them through a `predicate` |
| * function and only emits those values that yielded `true`. |
| * |
| * ## Example |
| * Emit only click events whose target was a DIV element |
| * ```ts |
| * import { fromEvent } from 'rxjs'; |
| * import { filter } from 'rxjs/operators'; |
| * |
| * const clicks = fromEvent(document, 'click'); |
| * const clicksOnDivs = clicks.pipe(filter(ev => ev.target.tagName === 'DIV')); |
| * clicksOnDivs.subscribe(x => console.log(x)); |
| * ``` |
| * |
| * @see {@link distinct} |
| * @see {@link distinctUntilChanged} |
| * @see {@link distinctUntilKeyChanged} |
| * @see {@link ignoreElements} |
| * @see {@link partition} |
| * @see {@link skip} |
| * |
| * @param {function(value: T, index: number): boolean} predicate A function that |
| * evaluates each value emitted by the source Observable. If it returns `true`, |
| * the value is emitted, if `false` the value is not passed to the output |
| * Observable. The `index` parameter is the number `i` for the i-th source |
| * emission that has happened since the subscription, starting from the number |
| * `0`. |
| * @param {any} [thisArg] An optional argument to determine the value of `this` |
| * in the `predicate` function. |
| * @return {Observable} An Observable of values from the source that were |
| * allowed by the `predicate` function. |
| * @method filter |
| * @owner Observable |
| */ |
| export function filter<T>(predicate: (value: T, index: number) => boolean, |
| thisArg?: any): MonoTypeOperatorFunction<T> { |
| return function filterOperatorFunction(source: Observable<T>): Observable<T> { |
| return source.lift(new FilterOperator(predicate, thisArg)); |
| }; |
| } |
| |
| class FilterOperator<T> implements Operator<T, T> { |
| constructor(private predicate: (value: T, index: number) => boolean, |
| private thisArg?: any) { |
| } |
| |
| call(subscriber: Subscriber<T>, source: any): TeardownLogic { |
| return source.subscribe(new FilterSubscriber(subscriber, this.predicate, this.thisArg)); |
| } |
| } |
| |
| /** |
| * We need this JSDoc comment for affecting ESDoc. |
| * @ignore |
| * @extends {Ignored} |
| */ |
| class FilterSubscriber<T> extends Subscriber<T> { |
| |
| count: number = 0; |
| |
| constructor(destination: Subscriber<T>, |
| private predicate: (value: T, index: number) => boolean, |
| private thisArg: any) { |
| super(destination); |
| } |
| |
| // the try catch block below is left specifically for |
| // optimization and perf reasons. a tryCatcher is not necessary here. |
| protected _next(value: T) { |
| let result: any; |
| try { |
| result = this.predicate.call(this.thisArg, value, this.count++); |
| } catch (err) { |
| this.destination.error(err); |
| return; |
| } |
| if (result) { |
| this.destination.next(value); |
| } |
| } |
| } |