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1 | 1 | import { OperatorDoc } from '../operator.model';
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2 | 2 |
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3 | 3 | export const forkJoin: OperatorDoc = {
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4 |
| - 'name': 'forkJoin', |
5 |
| - 'operatorType': 'combination' |
| 4 | + name: 'forkJoin', |
| 5 | + operatorType: 'combination', |
| 6 | + signature: 'public static forkJoin(sources: *): any', |
| 7 | + parameters: [ |
| 8 | + { |
| 9 | + name: 'sources', |
| 10 | + type: '*', |
| 11 | + attribute: '', |
| 12 | + description: '' |
| 13 | + } |
| 14 | + ], |
| 15 | + marbleUrl: 'http://reactivex.io/rxjs/img/forkJoin.png', |
| 16 | + shortDescription: { |
| 17 | + description: 'Joins last values emitted by passed Observables.', |
| 18 | + extras: [ |
| 19 | + { |
| 20 | + type: 'Tip', |
| 21 | + text: |
| 22 | + 'Wait for Observables to complete and then combine last values they emitted.' |
| 23 | + } |
| 24 | + ] |
| 25 | + }, |
| 26 | + walkthrough: { |
| 27 | + description: ` |
| 28 | + <p> |
| 29 | + <span class="markdown-code">forkJoin</span> is an operator that takes any number of |
| 30 | + Observables which can be passed either as an array or directly as arguments. If no input |
| 31 | + Observables are provided, resulting stream will complete immediately. |
| 32 | + </p> |
| 33 | + <p> |
| 34 | + <span class="markdown-code">forkJoin</span> will wait for all passed Observables to complete |
| 35 | + and then it will emit an array with last values from corresponding Observables. So if you |
| 36 | + pass "n" Observables to the operator, resulting array will have "n" values, where first |
| 37 | + value is the last thing emitted by the first Observable, second value is the last thing |
| 38 | + emitted by the second Observable and so on. That means <span class="markdown-code">forkJoin</span> will |
| 39 | + not emit more than once and it will complete after that. If you need to emit combined values not only |
| 40 | + at the end of lifecycle of passed Observables, but also throughout it, try out |
| 41 | + <a href='/#/operators/combineLatest' class='markdown-code'>combineLatest</a> |
| 42 | + or <a href='/#/operators/zip' class='markdown-code'>zip</a> instead. |
| 43 | + </p> |
| 44 | + <p> |
| 45 | + In order for resulting array to have the same length as the number of input Observables, whenever any of that |
| 46 | + Observables completes without emitting any value, |
| 47 | + <span class="markdown-code">forkJoin</span> will complete at that moment as well and it will not |
| 48 | + emit anything either, even if it already has some last values from other Observables. |
| 49 | + </p> |
| 50 | +
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| 51 | + <p> |
| 52 | + Conversely, if there is an Observable that never completes, |
| 53 | + <span class="markdown-code">forkJoin</span> will never complete as well, unless at |
| 54 | + any point some other Observable completes without emitting value, which brings us back to the previous case. |
| 55 | + Overall, in order for <span class="markdown-code">forkJoin</span> to emit a value, all Observables passed as arguments |
| 56 | + have to emit something at least once and complete. |
| 57 | + </p> |
| 58 | + <p> |
| 59 | + If any input Observable errors at some point, <span class="markdown-code">forkJoin</span> |
| 60 | + will error as well and all other Observables |
| 61 | + will be immediately unsubscribed. |
| 62 | + </p> |
| 63 | + <p> |
| 64 | + Optionally <span class="markdown-code">forkJoin</span> accepts project function, that will be |
| 65 | + called with values which normally would land in emitted array. Whatever is returned by project function, |
| 66 | + will appear in output Observable instead. This means that default project can be thought of as a |
| 67 | + function that takes all its arguments and puts them into an array. Note that project function will be called only |
| 68 | + when output Observable is supposed to emit a result. |
| 69 | + </p> |
| 70 | + ` |
| 71 | + }, |
| 72 | + examples: [ |
| 73 | + { |
| 74 | + name: 'Use forkJoin with operator emitting immediately', |
| 75 | + code: ` |
| 76 | + const observable = Rx.Observable.forkJoin( |
| 77 | + Rx.Observable.of(1, 2, 3, 4), |
| 78 | + Rx.Observable.of(5, 6, 7, 8) |
| 79 | + ); |
| 80 | + observable.subscribe( |
| 81 | + value => console.log(value), |
| 82 | + err => {}, |
| 83 | + () => console.log('This is how it ends!') |
| 84 | + ); |
| 85 | + // Logs: |
| 86 | + // [4, 8] |
| 87 | + // "This is how it ends!" |
| 88 | + `, |
| 89 | + externalLink: { |
| 90 | + platform: 'JSBin', |
| 91 | + url: 'http://jsbin.com/kinilaruki/1/embed?js,console' |
| 92 | + } |
| 93 | + }, |
| 94 | + { |
| 95 | + name: 'Use forkJoin with operator emitting after some time', |
| 96 | + code: ` |
| 97 | + const observable = Rx.Observable.forkJoin( |
| 98 | + Rx.Observable.interval(1000).take(3), // emit 0, 1, 2 every second and complete |
| 99 | + Rx.Observable.interval(500).take(4) // emit 0, 1, 2, 3 every half a second and complete |
| 100 | + ); |
| 101 | + observable.subscribe( |
| 102 | + value => console.log(value), |
| 103 | + err => {}, |
| 104 | + () => console.log('This is how it ends!') |
| 105 | + ); |
| 106 | + // Logs: |
| 107 | + // [2, 3] after 3 seconds |
| 108 | + // "This is how it ends!" immediately after |
| 109 | + `, |
| 110 | + externalLink: { |
| 111 | + platform: 'JSBin', |
| 112 | + url: 'http://jsbin.com/rewivubuqi/1/embed?js,console' |
| 113 | + } |
| 114 | + }, |
| 115 | + { |
| 116 | + name: 'Use forkJoin with project function', |
| 117 | + code: ` |
| 118 | + const observable = Rx.Observable.forkJoin( |
| 119 | + Rx.Observable.interval(1000).take(3), // emit 0, 1, 2 every second and complete |
| 120 | + Rx.Observable.interval(500).take(4), // emit 0, 1, 2, 3 every half a second and complete |
| 121 | + (n, m) => n + m |
| 122 | + ); |
| 123 | + observable.subscribe( |
| 124 | + value => console.log(value), |
| 125 | + err => {}, |
| 126 | + () => console.log('This is how it ends!') |
| 127 | + ); |
| 128 | + // Logs: |
| 129 | + // 5 after 3 seconds |
| 130 | + // "This is how it ends!" immediately after |
| 131 | + `, |
| 132 | + externalLink: { |
| 133 | + platform: 'JSBin', |
| 134 | + url: 'http://jsbin.com/wayomumike/1/embed?js,console' |
| 135 | + } |
| 136 | + } |
| 137 | + ], |
| 138 | + relatedOperators: ['combineLatest', 'zip'] |
6 | 139 | };
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