day_1.js

var fs = require('fs');
var timeStarted = Date.now();

fs.readFile('input_1.txt', 'utf-8', function(err, text) {
  if (err) {
    console.error(err);
    process.exit(1);
  }
  else {
    let inputs = text.trim().split('\n');
    let totalFuel = 0;
    inputs.forEach(function(mass) {
      totalFuel += _calculateTotalFuelRequirement(mass);
    });
    console.log('Total fuel requirement', totalFuel);
    console.log('Processed in', Date.now() - timeStarted, 'ms');
    process.exit(0);
  }
})

function _calculateFuelRequirement(mass) {
  return parseInt(parseInt(mass) / 3) - 2;
}

function _calculateTotalFuelRequirement(mass) {
  let initialCost = _calculateFuelRequirement(mass);
  let totalFuel = initialCost;
  while (initialCost > 0) {
    let newFuelCost = _calculateFuelRequirement(initialCost);
    if (newFuelCost > 0) totalFuel += newFuelCost;
    initialCost = newFuelCost;
  }
  return totalFuel;
}