axax/esnext/debounce.js

A library of async iterator extensions for JavaScript including ```map```, ```reduce```, ```filter```, ```flatMap```, ```pipe``` and [more](https://github.com/jamiemccrindle/axax/blob/master/docs/API.md#functions).

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
/**
 * Debounce an async iterator. Only emit values when no new value has been received during the provided timer duration.
 */
function debounce(timer) {
    return async function* inner(source) {
        const sourceIterator = source[Symbol.asyncIterator]();
        let itemPromise = sourceIterator.next();
        let pendingTimerPromise = null;
        let item = await itemPromise;
        let previousItem = item;
        while (!item.done) {
            pendingTimerPromise = pendingTimerPromise || timer(item.value);
            const raceResult = await Promise.race([itemPromise, pendingTimerPromise]);
            // raceResult is the value of the first promise to resolve. If raceResult
            // is not undefined, it _should_ be the result of the itemPromise since
            // pendingTimerPromise resolves to void. Just to be sure though, we check
            // that the result has the shape of an IteratorResult.
            if (raceResult && raceResult.hasOwnProperty("value") && raceResult.hasOwnProperty("done")) {
                // itemPromise won the race!
                previousItem = item;
                item = raceResult;
                itemPromise = sourceIterator.next();
            }
            else {
                // pendingTimerPromise won the race!
                yield item.value;
                pendingTimerPromise = null;
                previousItem = item;
                item = await itemPromise;
                itemPromise = sourceIterator.next();
            }
        }
        if (pendingTimerPromise) {
            await pendingTimerPromise;
            yield previousItem.value;
        }
    };
}
exports.debounce = debounce;