non-blocking.js

console.log('start');
const fs = require('fs');
var data = '';
fs.readFile('test.txt', (err, result) => {
  if (err) {
    throw err;
  } else {
    console.log('complete now')
    data = result;
  }
});
console.log('end');

# output
# ----------
# start
# end
# complete now