ix/asynciterable/fromeventpattern.mjs

The Interactive Extensions for JavaScript

import { __asyncGenerator, __await } from "tslib";
import { memoize } from './operators/memoize.mjs';
import { identity } from '../util/identity.mjs';
import { isFunction } from '../util/isiterable.mjs';
import { AsyncSink } from './asyncsink.mjs';
const { isArray } = Array;
function callOrApply(fn, args) {
    return isArray(args) ? fn(...args) : fn(args);
}
/**
 * Creates async-iterable from an event emitter by adding handlers for both listening and unsubscribing from events.
 *
 * @template TSource The type of elements in the event emitter.
 * @param {(handler: (...args: any[]) => void) => void} addHandler The function to add a listener to the source.
 * @param {(handler: (...args: any[]) => void) => void} removeHandler The function to remove a listener from the source.
 * @returns {AsyncIterableX<TSource>} An async-iterable which contains the data from the underlying events as wrapped by the handlers.
 */
export function fromEventPattern(addHandler, removeHandler, resultSelector) {
    if (!isFunction(resultSelector)) {
        resultSelector = identity;
    }
    const sink = new AsyncSink();
    const handler = (...args) => sink.write(callOrApply(resultSelector, args));
    addHandler(handler);
    const loop = function () {
        return __asyncGenerator(this, arguments, function* () {
            try {
                for (let next; !(next = yield __await(sink.next())).done;) {
                    yield yield __await(next.value);
                }
            }
            finally {
                removeHandler(handler);
                sink.end();
            }
        });
    };
    return memoize()(loop());
}

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