app.js

// Hello. I'm learning. Thank you for sharing your insights.
var sUtil = require('sUtils.js');

var obj = {
  a:[1,2],
  b:[3,4],
}

Object.keys(obj).forEach(function(key) {
  if (Array.isArray(obj[key])) {
    obj[key] = sUtil.bitmaskArrayToDecimal(obj[key]);
  }
});

sUtils.js

var bitmaskArrayToDecimal = export = function (arr) {
	var result = 0;
	for (var i = 0; i < arr.length; i++) {
		result = result | (1 << arr[i] - 1);
	};
	return result;
}