[рони]

JavDev,

var max = "9999" , min = "9";

function difference(max, min) {
      max = max.split('')
          .reverse();
      max.push(0);
      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 > 9 ? (c = (b/10|0), b % 10) : (c = 0, b)
      }
      return result.reverse()
          .join('')
          .replace(/^0+/, '');
  }
 alert(difference(max,min) )