How to process .JS files individually in a synchronously fashion one by one in node js after each one of them have finished their tasks?

Question

I have a set of .js files which perform certain tasks. Id like to process this files individually in a synchronously fashion after each one of them had finished their tasks.

Right now when I run my code all functions perform perfectly, yet in an async way. Im afraid I have also tried with promises (take a look at //FILE parent v2 in code) yet it seems that nonetheless the task being executed in order yet not waiting to be processed one after the other.

I´m pretty sure there must be a basic solution to that issue. yet my programming skills are scarce.

thanks for understanding.

right now my code looks like this:

 //FILE parent.js const cp = require('child_process'); const path = require('path'); //PROCESS1 var child_call = cp.fork("process1.js") child_call.on("exit", () => { console.log("1st funtion finished"); }) //PROCESS2 var child_capture = cp.fork("process2.js") child_capture.on("exit", () => { console.log("2nd funtion finished"); }) //PROCESS3 var child_render = cp.fork("process3.js") child_render.on("exit", () => { console.log("3rd funtion finished"); }) //FILE v2 Promisess parent.js const async = require('async'); const cp = require('child_process'); const path = require('path'); function addPromise() { return new Promise(resolve => { var child_call = cp.fork("process1.js") child_call.on("exit", () => { console.log("1st funtion finished"); }) resolve() }); } function addCapture() { return new Promise(resolve => { var child_capture = cp.fork("process2.js") child_capture.on("exit", () => { console.log("2nd funtion finished"); }) resolve() }); } function addRender() { return new Promise(resolve => { var child_render = cp.fork("process3.js") child_render.on("exit", () => { console.log("3rd funtion finished"); }) resolve() }); } async function addAsync() { const a = await addPromise(); const b = await addCapture(); const c = await addRender(); return a + b + c; } addAsync().then((sum) => { console.log(sum); }); 

Answer 1

require and module.exports

One solution that immediately jumps out is to use require instead of using child_process.fork . This way your imported code will run synchronously and you will get a direct output returned.

Example:

function add() {
  const a = require('a.js');
  const b = require('b.js');
  const c = require('c.js');
  return a + b + c;
}

// or you can make it more usable
function addModules(...fileNames) {
  return fileNames
    .map(fileName => require(fileName))
    .reduce((total, x) => total + x, 0);
}

Do note that you will be required to export your results from those files if you wish to use them.

// Do your stuff here:
const x = 42;

// Export it
module.exports = x;

Or you can use deasync

Deasync allows you to run a promise synchronously by passing that function to it.

Example:

const cp = require('child_process');
const deasync = require('deasync');

const fork = deasync(cp.fork);

function addPromise() {
  const child_call = fork('process1.js');
  // now synchronous
};
// repeat as needed

function add() {
  const a = addPromise();
  // ...
  return a + b + c;
}

Note: deasync exposes implementation details of Node.js at the language level and as such shouldn't be used unless other safer solutions don't work for you.