wed/standalone/lib/external/rxjs/internal/operators/first.js

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define(function(require,exports,module){

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var EmptyError_1 = require("../util/EmptyError");
var filter_1 = require("./filter");
var take_1 = require("./take");
var defaultIfEmpty_1 = require("./defaultIfEmpty");
var throwIfEmpty_1 = require("./throwIfEmpty");
var identity_1 = require("../util/identity");
/**
 * Emits only the first value (or the first value that meets some condition)
 * emitted by the source Observable.
 *
 * <span class="informal">Emits only the first value. Or emits only the first
 * value that passes some test.</span>
 *
 * <img src="./img/first.png" width="100%">
 *
 * If called with no arguments, `first` emits the first value of the source
 * Observable, then completes. If called with a `predicate` function, `first`
 * emits the first value of the source that matches the specified condition. It
 * may also take a `resultSelector` function to produce the output value from
 * the input value, and a `defaultValue` to emit in case the source completes
 * before it is able to emit a valid value. Throws an error if `defaultValue`
 * was not provided and a matching element is not found.
 *
 * @example <caption>Emit only the first click that happens on the DOM</caption>
 * var clicks = Rx.Observable.fromEvent(document, 'click');
 * var result = clicks.first();
 * result.subscribe(x => console.log(x));
 *
 * @example <caption>Emits the first click that happens on a DIV</caption>
 * var clicks = Rx.Observable.fromEvent(document, 'click');
 * var result = clicks.first(ev => ev.target.tagName === 'DIV');
 * result.subscribe(x => console.log(x));
 *
 * @see {@link filter}
 * @see {@link find}
 * @see {@link take}
 *
 * @throws {EmptyError} Delivers an EmptyError to the Observer's `error`
 * callback if the Observable completes before any `next` notification was sent.
 *
 * @param {function(value: T, index: number, source: Observable<T>): boolean} [predicate]
 * An optional function called with each item to test for condition matching.
 * @param {R} [defaultValue] The default value emitted in case no valid value
 * was found on the source.
 * @return {Observable<T|R>} An Observable of the first item that matches the
 * condition.
 * @method first
 * @owner Observable
 */
function first(predicate, defaultValue) {
    var hasDefaultValue = arguments.length >= 2;
    return function (source) { return source.pipe(predicate ? filter_1.filter(function (v, i) { return predicate(v, i, source); }) : identity_1.identity, take_1.take(1), hasDefaultValue ? defaultIfEmpty_1.defaultIfEmpty(defaultValue) : throwIfEmpty_1.throwIfEmpty(function () { return new EmptyError_1.EmptyError(); })); };
}
exports.first = first;
//# sourceMappingURL=first.js.map
return module.exports;

});