簡單工廠（Single Factory）在JavaScript中簡單實現

      var SingleFactory = function() {
          function Operation() {
              this.A = 0;
              this.B = 0;
          }

          OperationAdd.prototype = new Operation();
          OperationSub.prototype = new Operation();

          function OperationAdd() {
              this.getResult = function() {
                  return this.A + this.B;
              }
          }

          function OperationSub() {
              this.getResult = function() {
                  return this.A - this.B;
              }
          }

          function OperationFactory(arg) {
              var ret = null;
              switch (arg) {
                  case '+':
                      ret = new OperationAdd();
                      break;
                  case '-':
                      ret = new OperationSub();
                      break;
                  default:
                      alert(arg);
                      break;
              }
              return ret;
          }

          var a = new OperationFactory('+');
          a.A = 10;
          a.B = 20;
          alert(a.getResult());
      }