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Reactive Extensions for modern JavaScript
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<div class="content" data-ice="content"><h1 data-ice="title">es6/operator/elementAt.js</h1>
<pre class="source-code line-number raw-source-code"><code class="prettyprint linenums" data-ice="content">import { Subscriber } from '../Subscriber';
import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError';
/**
* Emits the single value at the specified `index` in a sequence of emissions
* from the source Observable.
*
* <span class="informal">Emits only the i-th value, then completes.</span>
*
* <img src="./img/elementAt.png" width="100%">
*
* `elementAt` returns an Observable that emits the item at the specified
* `index` in the source Observable, or a default value if that `index` is out
* of range and the `default` argument is provided. If the `default` argument is
* not given and the `index` is out of range, the output Observable will emit an
* `ArgumentOutOfRangeError` error.
*
* @example <caption>Emit only the third click event</caption>
* var clicks = Rx.Observable.fromEvent(document, 'click');
* var result = clicks.elementAt(2);
* result.subscribe(x => console.log(x));
*
* @see {@link first}
* @see {@link last}
* @see {@link skip}
* @see {@link single}
* @see {@link take}
*
* @throws {ArgumentOutOfRangeError} When using `elementAt(i)`, it delivers an
* ArgumentOutOrRangeError to the Observer's `error` callback if `i < 0` or the
* Observable has completed before emitting the i-th `next` notification.
*
* @param {number} index Is the number `i` for the i-th source emission that has
* happened since the subscription, starting from the number `0`.
* @param {T} [defaultValue] The default value returned for missing indices.
* @return {Observable} An Observable that emits a single item, if it is found.
* Otherwise, will emit the default value if given. If not, then emits an error.
* @method elementAt
* @owner Observable
*/
export function elementAt(index, defaultValue) {
return this.lift(new ElementAtOperator(index, defaultValue));
}
var ElementAtOperator = (function () {
function ElementAtOperator(index, defaultValue) {
this.index = index;
this.defaultValue = defaultValue;
if (index < 0) {
throw new ArgumentOutOfRangeError;
}
}
ElementAtOperator.prototype.call = function (subscriber, source) {
return source._subscribe(new ElementAtSubscriber(subscriber, this.index, this.defaultValue));
};
return ElementAtOperator;
}());
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
var ElementAtSubscriber = (function (_super) {
__extends(ElementAtSubscriber, _super);
function ElementAtSubscriber(destination, index, defaultValue) {
_super.call(this, destination);
this.index = index;
this.defaultValue = defaultValue;
}
ElementAtSubscriber.prototype._next = function (x) {
if (this.index-- === 0) {
this.destination.next(x);
this.destination.complete();
}
};
ElementAtSubscriber.prototype._complete = function () {
var destination = this.destination;
if (this.index >= 0) {
if (typeof this.defaultValue !== 'undefined') {
destination.next(this.defaultValue);
}
else {
destination.error(new ArgumentOutOfRangeError);
}
}
destination.complete();
};
return ElementAtSubscriber;
}(Subscriber));
//# sourceMappingURL=elementAt.js.map</code></pre>
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