when to use child process in node js code example

Example 1: how to return when child process is complete in node js

var child = require('child_process').exec('python celulas.py')
child.stdout.pipe(process.stdout)
child.on('exit', function() {
  process.exit()
})

Example 2: how to return when child process is complete in node js

var execSync = require('exec-sync');

var user = execSync('python celulas.py');