Simple Queue Implemenation in JS

queue.js

// --------
// USAGE
// --------
const q = queue({
    onJobComplete: ({alias, result})=>{
        console.log(`Completed job ${alias} with result: `, result);
    },
    onJobFail: ({alias, error})=>{
        console.error(`Job ${alias} had error: `, error);
    }
});

q.submitJob('job1', function({ alias }){
    console.log(`We start job ${alias} ...`);
    return _delay(3000).then(_=>{
        console.log(`Finished job 1 after 3 seconds...`);
        return `solution 1`;
    });
})

q.submitJob('job1failure', ()=>{
    return _delay(1000).then(result=>{
        throw new Error(`This is simulated  error`);
    });
});


q.submitJob('job2', function({ alias }){
    console.log(`We start job ${alias} ...`);
    return _delay(2000).then(_=>{
        console.log(`Finished job 2 after 2 seconds...`);
        return `solution2`;
    });  
});


// --------
// IMPLEMENTATION
// --------
function queue({ onJobComplete, onJobFail , quitOnDrain = true, drainTimeout = 1000}){

    const noop = ()=>{};
    onJobComplete = onJobComplete ||  noop;
    onJobFail = onJobFail || noop;


    let queueTickets = [];
    let jobInProgress = null;
    let resultHistory = [];

    let lastDrainTs = null;

    let iv = setInterval(() => {
        if ( jobInProgress ) return;
        if ( queueTickets.length < 1 ) {
            checkStop();
            return;
        }
        else{
            lastDrainTs = null;
        }
        let ticket;
        let { alias, jobFn } = ticket = queueTickets.shift();
        jobInProgress = ticket;
        Promise.resolve(jobFn(ticket))
            .then(result=>{
                jobInProgress = null;
                let receipt = { alias, result };
                resultHistory.push(receipt);
                onJobComplete(receipt);
            })
            .catch(error=>{
                jobInProgress = null;
                let receipt = { alias, error };
                resultHistory.push(receipt);
                onJobFail(receipt);
            });
    }, 100);


    function checkStop(){
        if ( !lastDrainTs ) { // first time drain detected
            lastDrainTs =  new Date();
            return;
        }
        let now = new Date();
        if ( now.getTime() - lastDrainTs.getTime()  > drainTimeout){
            clearInterval(iv);
        }
        else{
            // console.log(`Waiting for drain timeout...`);
        }
    }

    const api = {

        submitJob(alias, jobFn){
            queueTickets.push({ alias, jobFn});
            console.log(`Submitted job ${alias}. Total jobs: ${queueTickets.length}`);
            return api;
        }
    };
    return api;
}


// --------
// UTILS
// --------
function _delay(millis){
    return new Promise(resolve=>setTimeout(resolve, millis));
}