Synchronous Fork in Node.js (with async.series): wait for child_process.fork to finish, then execute part2

fork-sync.js

var fs = require('fs');
var fork = require('child_process').fork;
var async = require('async');

async.series([
    function(callback){ 
        var command = fork("./command.js", [], {silent: true }); 
        command.stdout.pipe(process.stdout);
        command.stderr.pipe(process.stderr);
        
        //CREATE write file for stdout, LISTEN to stdout, WRITE to file
        var file = fs.createWriteStream('./progress.txt');
        command.stdout.on('data', function(data) {file.write(data);});
        command.stderr.on('data', function(data) {file.write(data);});
        command.stdout.on('end', function(data) {file.end();});
        command.stderr.on('end', function(data) {file.end();});
        
        //when child process exits, check if there were any errors and close the writeable stream
        command.on('exit', function(code) {
            if (code !== 0) {console.log('Failed: ' + code);}
            callback();
        });
        
    },
    function(callback){ 
        console.log('PART2');
        callback();
    }
]);

Hardest Part: putting the callback(); inside the command.on 'exit' function

By doing this, the script will wait until the fork is finished before moving onto PART2

REFERENCES
https://github.com/caolan/async

Sounds great, but the callback is compulsory or not?

Unfortunately, the callback is compulsory due to the use of the async library. See the documentation here: https://caolan.github.io/async/v3/docs.html#series