wed
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Wed is a schema-aware editor for XML documents.
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JavaScript
define(function(require,exports,module){
/** PURE_IMPORTS_START _util_EmptyError,_filter,_take,_defaultIfEmpty,_throwIfEmpty,_util_identity PURE_IMPORTS_END */
import { EmptyError } from '../util/EmptyError';
import { filter } from './filter';
import { take } from './take';
import { defaultIfEmpty } from './defaultIfEmpty';
import { throwIfEmpty } from './throwIfEmpty';
import { identity } from '../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
*/
export function first(predicate, defaultValue) {
var hasDefaultValue = arguments.length >= 2;
return function (source) { return source.pipe(predicate ? filter(function (v, i) { return predicate(v, i, source); }) : identity, take(1), hasDefaultValue ? defaultIfEmpty(defaultValue) : throwIfEmpty(function () { return new EmptyError(); })); };
}
//# sourceMappingURL=first.js.map
return module.exports;
});