78 lines
2.7 KiB
JavaScript
78 lines
2.7 KiB
JavaScript
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import { Subscriber } from '../Subscriber';
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/**
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* Applies a given `project` function to each value emitted by the source
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* Observable, and emits the resulting values as an Observable.
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*
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* <span class="informal">Like [Array.prototype.map()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map),
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* it passes each source value through a transformation function to get
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* corresponding output values.</span>
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*
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* <img src="./img/map.png" width="100%">
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*
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* Similar to the well known `Array.prototype.map` function, this operator
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* applies a projection to each value and emits that projection in the output
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* Observable.
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*
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* @example <caption>Map every click to the clientX position of that click</caption>
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* var clicks = Rx.Observable.fromEvent(document, 'click');
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* var positions = clicks.map(ev => ev.clientX);
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* positions.subscribe(x => console.log(x));
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*
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* @see {@link mapTo}
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* @see {@link pluck}
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*
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* @param {function(value: T, index: number): R} project The function to apply
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* to each `value` emitted by the source Observable. The `index` parameter is
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* the number `i` for the i-th emission that has happened since the
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* subscription, starting from the number `0`.
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* @param {any} [thisArg] An optional argument to define what `this` is in the
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* `project` function.
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* @return {Observable<R>} An Observable that emits the values from the source
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* Observable transformed by the given `project` function.
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* @method map
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* @owner Observable
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*/
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export function map(project, thisArg) {
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return function mapOperation(source) {
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if (typeof project !== 'function') {
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throw new TypeError('argument is not a function. Are you looking for `mapTo()`?');
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}
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return source.lift(new MapOperator(project, thisArg));
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};
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}
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export class MapOperator {
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constructor(project, thisArg) {
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this.project = project;
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this.thisArg = thisArg;
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}
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call(subscriber, source) {
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return source.subscribe(new MapSubscriber(subscriber, this.project, this.thisArg));
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}
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}
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/**
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* We need this JSDoc comment for affecting ESDoc.
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* @ignore
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* @extends {Ignored}
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*/
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class MapSubscriber extends Subscriber {
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constructor(destination, project, thisArg) {
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super(destination);
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this.project = project;
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this.count = 0;
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this.thisArg = thisArg || this;
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}
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// NOTE: This looks unoptimized, but it's actually purposefully NOT
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// using try/catch optimizations.
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_next(value) {
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let result;
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try {
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result = this.project.call(this.thisArg, value, this.count++);
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}
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catch (err) {
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this.destination.error(err);
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return;
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}
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this.destination.next(result);
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}
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}
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//# sourceMappingURL=map.js.map
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