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56 lines
2.5 KiB
56 lines
2.5 KiB
"use strict"; |
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var first_1 = require('../operators/first'); |
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/** |
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* Emits only the first value (or the first value that meets some condition) |
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* emitted by the source Observable. |
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* |
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* <span class="informal">Emits only the first value. Or emits only the first |
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* value that passes some test.</span> |
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* |
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* <img src="./img/first.png" width="100%"> |
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* |
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* If called with no arguments, `first` emits the first value of the source |
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* Observable, then completes. If called with a `predicate` function, `first` |
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* emits the first value of the source that matches the specified condition. It |
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* may also take a `resultSelector` function to produce the output value from |
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* the input value, and a `defaultValue` to emit in case the source completes |
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* before it is able to emit a valid value. Throws an error if `defaultValue` |
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* was not provided and a matching element is not found. |
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* |
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* @example <caption>Emit only the first click that happens on the DOM</caption> |
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* var clicks = Rx.Observable.fromEvent(document, 'click'); |
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* var result = clicks.first(); |
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* result.subscribe(x => console.log(x)); |
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* |
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* @example <caption>Emits the first click that happens on a DIV</caption> |
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* var clicks = Rx.Observable.fromEvent(document, 'click'); |
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* var result = clicks.first(ev => ev.target.tagName === 'DIV'); |
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* result.subscribe(x => console.log(x)); |
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* |
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* @see {@link filter} |
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* @see {@link find} |
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* @see {@link take} |
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* |
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* @throws {EmptyError} Delivers an EmptyError to the Observer's `error` |
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* callback if the Observable completes before any `next` notification was sent. |
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* |
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* @param {function(value: T, index: number, source: Observable<T>): boolean} [predicate] |
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* An optional function called with each item to test for condition matching. |
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* @param {function(value: T, index: number): R} [resultSelector] A function to |
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* produce the value on the output Observable based on the values |
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* and the indices of the source Observable. The arguments passed to this |
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* function are: |
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* - `value`: the value that was emitted on the source. |
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* - `index`: the "index" of the value from the source. |
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* @param {R} [defaultValue] The default value emitted in case no valid value |
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* was found on the source. |
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* @return {Observable<T|R>} An Observable of the first item that matches the |
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* condition. |
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* @method first |
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* @owner Observable |
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*/ |
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function first(predicate, resultSelector, defaultValue) { |
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return first_1.first(predicate, resultSelector, defaultValue)(this); |
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} |
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exports.first = first; |
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//# sourceMappingURL=first.js.map
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