@reactivex/rxjs
Version:
Reactive Extensions for modern JavaScript
125 lines • 4.5 kB
JavaScript
;
var __extends = (this && this.__extends) || (function () {
var extendStatics = function (d, b) {
extendStatics = Object.setPrototypeOf ||
({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
return extendStatics(d, b);
}
return function (d, b) {
extendStatics(d, b);
function __() { this.constructor = d; }
d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
})();
Object.defineProperty(exports, "__esModule", { value: true });
var Subscriber_1 = require("../Subscriber");
var ArgumentOutOfRangeError_1 = require("../util/ArgumentOutOfRangeError");
var empty_1 = require("../observable/empty");
/**
* Emits only the last `count` values emitted by the source Observable.
*
* <span class="informal">Remembers the latest `count` values, then emits those
* only when the source completes.</span>
*
* 
*
* `takeLast` returns an Observable that emits at most the last `count` values
* emitted by the source Observable. If the source emits fewer than `count`
* values then all of its values are emitted. This operator must wait until the
* `complete` notification emission from the source in order to emit the `next`
* values on the output Observable, because otherwise it is impossible to know
* whether or not more values will be emitted on the source. For this reason,
* all values are emitted synchronously, followed by the complete notification.
*
* ## Example
* Take the last 3 values of an Observable with many values
* ```ts
* import { range } from 'rxjs';
* import { takeLast } from 'rxjs/operators';
*
* const many = range(1, 100);
* const lastThree = many.pipe(takeLast(3));
* lastThree.subscribe(x => console.log(x));
* ```
*
* @see {@link take}
* @see {@link takeUntil}
* @see {@link takeWhile}
* @see {@link skip}
*
* @throws {ArgumentOutOfRangeError} When using `takeLast(i)`, it delivers an
* ArgumentOutOrRangeError to the Observer's `error` callback if `i < 0`.
*
* @param {number} count The maximum number of values to emit from the end of
* the sequence of values emitted by the source Observable.
* @return {Observable<T>} An Observable that emits at most the last count
* values emitted by the source Observable.
* @method takeLast
* @owner Observable
*/
function takeLast(count) {
return function takeLastOperatorFunction(source) {
if (count === 0) {
return empty_1.empty();
}
else {
return source.lift(new TakeLastOperator(count));
}
};
}
exports.takeLast = takeLast;
var TakeLastOperator = /** @class */ (function () {
function TakeLastOperator(total) {
this.total = total;
if (this.total < 0) {
throw new ArgumentOutOfRangeError_1.ArgumentOutOfRangeError;
}
}
TakeLastOperator.prototype.call = function (subscriber, source) {
return source.subscribe(new TakeLastSubscriber(subscriber, this.total));
};
return TakeLastOperator;
}());
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
var TakeLastSubscriber = /** @class */ (function (_super) {
__extends(TakeLastSubscriber, _super);
function TakeLastSubscriber(destination, total) {
var _this = _super.call(this, destination) || this;
_this.total = total;
_this.ring = new Array();
_this.count = 0;
return _this;
}
TakeLastSubscriber.prototype._next = function (value) {
var ring = this.ring;
var total = this.total;
var count = this.count++;
if (ring.length < total) {
ring.push(value);
}
else {
var index = count % total;
ring[index] = value;
}
};
TakeLastSubscriber.prototype._complete = function () {
var destination = this.destination;
var count = this.count;
if (count > 0) {
var total = this.count >= this.total ? this.total : this.count;
var ring = this.ring;
for (var i = 0; i < total; i++) {
var idx = (count++) % total;
destination.next(ring[idx]);
}
}
destination.complete();
};
return TakeLastSubscriber;
}(Subscriber_1.Subscriber));
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