Serialize promises

promise-serializer.ts

// See: https://stackoverflow.com/questions/24586110/resolve-promises-one-after-another-i-e-in-sequence/31070150#31070150
//      https://decembersoft.com/posts/promises-in-serial-with-array-reduce/

/*
 * Serialize promises (or rather tasks because once created, a Promise starts executing immedialtely
 */
const promiseSerializer = (tasks: Array<()=>Promise<any>>) => {
    return tasks.reduce((promiseChain: Promise<any>, currentTask: ()=>Promise<any>) => {
        return promiseChain.then(chainResults =>
            currentTask().then(currentResult =>
                [...chainResults, currentResult]
            )
        );
    }, Promise.resolve([]));
};
  
// Demo
const promiseFactory = (code: number, delay: number = 2500) => {
    return new Promise((resolve, reject) => { 
        setTimeout(() => {
            console.log(new Date().toISOString(), code);
            resolve(code);
        }, delay);
    })
};

promiseSerializer([
    () => promiseFactory(42),
    () => promiseFactory(43),
    () => promiseFactory(44),
    () => promiseFactory(45)
]).then(values => { console.log(new Date().toISOString(), 'Results', values); });