reduce.js
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"use strict";
var __extends = (this && this.__extends) || function (d, b) {
for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
function __() { this.constructor = d; }
d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
var Subscriber_1 = require('../Subscriber');
/* tslint:disable:max-line-length */
/**
* Applies an accumulator function over the source Observable, and returns the
* accumulated result when the source completes, given an optional seed value.
*
* <span class="informal">Combines together all values emitted on the source,
* using an accumulator function that knows how to join a new source value into
* the accumulation from the past.</span>
*
* <img src="./img/reduce.png" width="100%">
*
* Like
* [Array.prototype.reduce()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce),
* `reduce` applies an `accumulator` function against an accumulation and each
* value of the source Observable (from the past) to reduce it to a single
* value, emitted on the output Observable. Note that `reduce` will only emit
* one value, only when the source Observable completes. It is equivalent to
* applying operator {@link scan} followed by operator {@link last}.
*
* Returns an Observable that applies a specified `accumulator` function to each
* item emitted by the source Observable. If a `seed` value is specified, then
* that value will be used as the initial value for the accumulator. If no seed
* value is specified, the first item of the source is used as the seed.
*
* @example <caption>Count the number of click events that happened in 5 seconds</caption>
* var clicksInFiveSeconds = Rx.Observable.fromEvent(document, 'click')
* .takeUntil(Rx.Observable.interval(5000));
* var ones = clicksInFiveSeconds.mapTo(1);
* var seed = 0;
* var count = ones.reduce((acc, one) => acc + one, seed);
* count.subscribe(x => console.log(x));
*
* @see {@link count}
* @see {@link expand}
* @see {@link mergeScan}
* @see {@link scan}
*
* @param {function(acc: R, value: T): R} accumulator The accumulator function
* called on each source value.
* @param {R} [seed] The initial accumulation value.
* @return {Observable<R>} An observable of the accumulated values.
* @return {Observable<R>} An Observable that emits a single value that is the
* result of accumulating the values emitted by the source Observable.
* @method reduce
* @owner Observable
*/
function reduce(accumulator, seed) {
var hasSeed = false;
// providing a seed of `undefined` *should* be valid and trigger
// hasSeed! so don't use `seed !== undefined` checks!
// For this reason, we have to check it here at the original call site
// otherwise inside Operator/Subscriber we won't know if `undefined`
// means they didn't provide anything or if they literally provided `undefined`
if (arguments.length >= 2) {
hasSeed = true;
}
return this.lift(new ReduceOperator(accumulator, seed, hasSeed));
}
exports.reduce = reduce;
var ReduceOperator = (function () {
function ReduceOperator(accumulator, seed, hasSeed) {
if (hasSeed === void 0) { hasSeed = false; }
this.accumulator = accumulator;
this.seed = seed;
this.hasSeed = hasSeed;
}
ReduceOperator.prototype.call = function (subscriber, source) {
return source.subscribe(new ReduceSubscriber(subscriber, this.accumulator, this.seed, this.hasSeed));
};
return ReduceOperator;
}());
exports.ReduceOperator = ReduceOperator;
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
var ReduceSubscriber = (function (_super) {
__extends(ReduceSubscriber, _super);
function ReduceSubscriber(destination, accumulator, seed, hasSeed) {
_super.call(this, destination);
this.accumulator = accumulator;
this.hasSeed = hasSeed;
this.hasValue = false;
this.acc = seed;
}
ReduceSubscriber.prototype._next = function (value) {
if (this.hasValue || (this.hasValue = this.hasSeed)) {
this._tryReduce(value);
}
else {
this.acc = value;
this.hasValue = true;
}
};
ReduceSubscriber.prototype._tryReduce = function (value) {
var result;
try {
result = this.accumulator(this.acc, value);
}
catch (err) {
this.destination.error(err);
return;
}
this.acc = result;
};
ReduceSubscriber.prototype._complete = function () {
if (this.hasValue || this.hasSeed) {
this.destination.next(this.acc);
}
this.destination.complete();
};
return ReduceSubscriber;
}(Subscriber_1.Subscriber));
exports.ReduceSubscriber = ReduceSubscriber;
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