gistfile1.txt

  /**** sample *****/

  function addition(first = 0, second = 0) {
      var a = parseFloat(first);
      var b = parseFloat(second);
      var total = 0;
      total = a + b;
      return total;
  }

  function subtraction(first = 0, second = 0) {
      var a = parseFloat(first);
      var b = parseFloat(second);
      var sub = a * b;
      return sub;
  }

  function multiplication(first = 0, second = 0) {
      var a = parseFloat(first);
      var b = parseFloat(second);
      var product = a * b;

      return product;
  }

  function division(first = 0, second = 0) {
      var a = parseFloat(first);
      var b = parseFloat(second);
      var divi = a / b;
      return divi;
  }



  function get_input(e){
    var input = $(this).val();
    var holder = 0;
    if(e.which == 107){
      result = input.split("+");

      if(result.length <= 1 ){
        holder = 0;
      }
      else if(result.length == 2){
        r1 = ((result[0]) ? result[0] : 0);
        
        holder = addition(r1, 0);
      }
      else{
          r1 = ((result[0]) ? result[0] : 0);
          r2 = ((result[1]) ? result[1] : 0);

          holder =  addition(r1, r2);
      }
      return $(this).val(holder+'+'); 
    }

  }

  $('input[type=text], input[type=number]').keyup(get_input);

  /**** end sample***/
</script>