[рони]

croatoan,
Вариант ...

var max = "10000000000000000000000000000" , min = "911";

function difference(max, min) {
      max = max.split('')
          .reverse();
      min = min.split('')
          .reverse();
      var len = max.length,
          result = [];
      for (var i = 0, b = 0, c = 0; i < len; i++) {
          b = max[i] - (min[i] || 0) + c;
          result[i] = b < 0 ? (c = -1, 10 + b) : (c = 0, b)
      }
      return result.reverse()
          .join('')
          .replace(/^0+/, '');
  }
 alert(difference(max,min) )