Reactor created by rowland - https://repl.it/FqqB/1

Reactor.js

function test (num) {
  var holder = num.split('');
  var sum = 0,  i = 0;
  var count = holder.length;
  while(i < count) {
   if(holder[i] === '-'){
     sum = sum - holder[i + 1];
     i += 2;
   } else{
     sum += parseInt(holder[i]);
     i++;
   }
  }
  return sum;
}
test('-4378384');