How to pass parameters in an array of functions using a series of promises

Question

I have the following functions of Promises:

const func1 = () => new Promise((resolve, reject) => {
    console.log('func1 start');
    setTimeout(() => {
        console.log('func1 complete');
        resolve('Hello');
    }, 1000);
});

const func2 = () => new Promise((resolve, reject) => {
    console.log('func2 start');
    setTimeout(() => {
        console.log('func2 complete');
        resolve('World');
    }, 2000);
});

And to execute those functions in series, I use:

const promiseSerial = funcs =>
  funcs.reduce((promise, func) =>
    promise.then(result => func().then(Array.prototype.concat.bind(result))),
    Promise.resolve([]))

And to call:

promiseSerial([func1, func2]).then(values => {
    console.log("Promise Resolved. " + values); // Promise Resolved. Hello, World
}, function(reason) {
    console.log("Promise Rejected. " + reason);
});

And everything works fine, because I can have an array of values in series according to the order of the functions.

So, my question is:

How can I pass parameters between functions? I mean, I want to pass a parameter from func1 to func2. I have thought maybe in the resolve, but it does not works.

Any ideas???

you can (and do) pass the resolved result of func1 to func2 - that's about all you can do — Jaromanda X
– Jaromanda X, Commented Sep 23, 2017 at 1:50

Rex Hsu · Accepted Answer · 2017-09-23 03:04:05Z

1

In func2() replace

const func2 = ()

to

const func2 = (PARAMETER)

In promiseSerial() replace

promise.then(result => func()

to

promise.then(result => func(result[0])

console.log the PARAMETER in func2 will show you the string 'Hello'

To send parameter to func1 and if you have multiple funcs

const func1 = (FIRST_PARA) => new Promise((resolve, reject) => {

  console.log('func1 start, the first parameter is ' + FIRST_PARA);
  setTimeout(() => {
    console.log('func1 complete');
    resolve('Hello');
  }, 1000);
});

const func2 = (FIRST_PARA, LAST_PARA) => new Promise((resolve, reject) => {

  console.log('func2 start, the received last parameter is ' + LAST_PARA);
  setTimeout(() => {
    console.log('func2 complete');
    resolve('World');
  }, 2000);
});

const promiseSerial = (funcs, firstParameter) => funcs.reduce((promise, func) =>
promise.then(result => func(firstParameter, result[result.length - 1]).then(Array.prototype.concat.bind(result))), Promise.resolve([]))


var firstParameter = 12;

promiseSerial([func1, func2], firstParameter).then(values => {
  console.log("Promise Resolved. " + values); // Promise Resolved. Hello, World
}, function(reason) {
  console.log("Promise Rejected. " + reason);
});

edited Sep 23, 2017 at 3:04

answered Sep 23, 2017 at 2:03

Rex Hsu

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3 Comments

robe007 Over a year ago

This is exactly what I'm needing. Thanks, works like a charms !

robe007 Over a year ago

Only one more thing: How can I put a parameter to the first function?

robe007 Over a year ago

Thanks my friend. Works perfectly !

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