asyncExecutor to limit the number of javascript async calls running at a given time

asyncExecutor.js

class AsyncAction{
    constructor(fn, args, resolveFn, rejectFn){
        this.fn = fn;
        this.args = args;
        this.resolveFn = resolveFn;
        this.rejectFn = rejectFn;
    }
}

export class AsyncExecutor{
    constructor(maxRunningActions){
        this.maxRunningActions = maxRunningActions;
        this.runningCounter = 0;
        this.pendingActions = [];
    }

    submit(fn, ...args){
        let resolveFn, rejectFn;
        let pr = new Promise((resFn, rejFn) => {
            resolveFn = resFn;
            rejectFn = rejFn;
        });
        let action = new AsyncAction(fn, args, resolveFn, rejectFn);

        if (this.runningCounter < this.maxRunningActions){
            this._runAction(action);
        }
        else{
            this.pendingActions.push(action);
        }

        return pr;
    }

    async _runAction(action){
        this.runningCounter++;
        let result;
        try{
            result = await action.fn(...(action.args));
        }
        catch (ex){
            this._processActionResult(action, false, ex);
            return;
        }
        this._processActionResult(action, true, result);
    }

    _processActionResult(action, successful /*bool*/, result){
        this.runningCounter--;
        if (successful){
            action.resolveFn(result);
        }
        else{
            action.rejectFn(result); //here result is an exception
        }
        if (this.pendingActions.length){
            this.runningCounter++;
            this._runAction(this.pendingActions.shift());
        }
    }
}

testAsyncExecutor.js

import {AsyncExecutor} from "./asyncExecutor.js"


function asyncSleep(interval){
    return new Promise(resFn => {
        setTimeout(resFn, interval);
    })
}

async function mockDownload(url, delay){
    console.log(`starting download: ${url}`);
    await asyncSleep(delay);
    return url.toUpperCase();
}

let executor = new AsyncExecutor(3);
let asyncDownloads = []
for (let i=0; i<= 6; i++){
    asyncDownloads.push(executor.submit(
        mockDownload, 
        `www.jesoutienslapolice.fr/post_${i}`, Math.floor(Math.random() * 4000)
    ).then(result => {
        console.log(`download ${i} finished`);
        return result;
    }));
    console.log("after submit");
}

let results = await Promise.all(asyncDownloads);
console.log(`results: ${JSON.stringify(results, null, "\t")}`);