1 | import { Operator } from '../Operator';
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2 | import { Subscriber } from '../Subscriber';
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3 | import { Observable } from '../Observable';
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4 | import { OperatorFunction, MonoTypeOperatorFunction, TeardownLogic } from '../types';
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5 |
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6 | /* tslint:disable:max-line-length */
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7 | export function filter<T, S extends T>(predicate: (value: T, index: number) => value is S,
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8 | thisArg?: any): OperatorFunction<T, S>;
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9 | export function filter<T>(predicate: (value: T, index: number) => boolean,
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10 | thisArg?: any): MonoTypeOperatorFunction<T>;
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11 | /* tslint:enable:max-line-length */
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12 |
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13 | /**
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14 | * Filter items emitted by the source Observable by only emitting those that
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15 | * satisfy a specified predicate.
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16 | *
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17 | * <span class="informal">Like
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18 | * [Array.prototype.filter()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter),
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19 | * it only emits a value from the source if it passes a criterion function.</span>
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20 | *
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21 | * ![](filter.png)
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22 | *
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23 | * Similar to the well-known `Array.prototype.filter` method, this operator
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24 | * takes values from the source Observable, passes them through a `predicate`
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25 | * function and only emits those values that yielded `true`.
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26 | *
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27 | * ## Example
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28 | * Emit only click events whose target was a DIV element
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29 | * ```ts
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30 | * import { fromEvent } from 'rxjs';
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31 | * import { filter } from 'rxjs/operators';
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32 | *
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33 | * const clicks = fromEvent(document, 'click');
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34 | * const clicksOnDivs = clicks.pipe(filter(ev => ev.target.tagName === 'DIV'));
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35 | * clicksOnDivs.subscribe(x => console.log(x));
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36 | * ```
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37 | *
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38 | * @see {@link distinct}
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39 | * @see {@link distinctUntilChanged}
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40 | * @see {@link distinctUntilKeyChanged}
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41 | * @see {@link ignoreElements}
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42 | * @see {@link partition}
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43 | * @see {@link skip}
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44 | *
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45 | * @param {function(value: T, index: number): boolean} predicate A function that
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46 | * evaluates each value emitted by the source Observable. If it returns `true`,
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47 | * the value is emitted, if `false` the value is not passed to the output
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48 | * Observable. The `index` parameter is the number `i` for the i-th source
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49 | * emission that has happened since the subscription, starting from the number
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50 | * `0`.
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51 | * @param {any} [thisArg] An optional argument to determine the value of `this`
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52 | * in the `predicate` function.
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53 | * @return {Observable} An Observable of values from the source that were
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54 | * allowed by the `predicate` function.
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55 | * @method filter
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56 | * @owner Observable
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57 | */
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58 | export function filter<T>(predicate: (value: T, index: number) => boolean,
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59 | thisArg?: any): MonoTypeOperatorFunction<T> {
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60 | return function filterOperatorFunction(source: Observable<T>): Observable<T> {
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61 | return source.lift(new FilterOperator(predicate, thisArg));
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62 | };
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63 | }
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64 |
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65 | class FilterOperator<T> implements Operator<T, T> {
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66 | constructor(private predicate: (value: T, index: number) => boolean,
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67 | private thisArg?: any) {
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68 | }
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69 |
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70 | call(subscriber: Subscriber<T>, source: any): TeardownLogic {
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71 | return source.subscribe(new FilterSubscriber(subscriber, this.predicate, this.thisArg));
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72 | }
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73 | }
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74 |
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75 | /**
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76 | * We need this JSDoc comment for affecting ESDoc.
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77 | * @ignore
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78 | * @extends {Ignored}
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79 | */
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80 | class FilterSubscriber<T> extends Subscriber<T> {
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81 |
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82 | count: number = 0;
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83 |
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84 | constructor(destination: Subscriber<T>,
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85 | private predicate: (value: T, index: number) => boolean,
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86 | private thisArg: any) {
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87 | super(destination);
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88 | }
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89 |
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90 | // the try catch block below is left specifically for
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91 | // optimization and perf reasons. a tryCatcher is not necessary here.
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92 | protected _next(value: T) {
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93 | let result: any;
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94 | try {
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95 | result = this.predicate.call(this.thisArg, value, this.count++);
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96 | } catch (err) {
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97 | this.destination.error(err);
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98 | return;
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99 | }
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100 | if (result) {
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101 | this.destination.next(value);
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102 | }
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103 | }
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104 | }
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