es6/operators/map.js

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