如下所示：<script language="javascript" type="text/javascript">
                        <!--                                
                                function myFun(x,y)
                                {
                                        if (arguments.length != 2)
                                        {
                                                var str = "传递的参数个数有误，一共传递了" + arguments.length + "个参数<br>";
                                                str += "传递过来的参数值分别为：<br>";
                                                for (i=0;i<arguments.length;i++)
                                                {
                                                        str += "第" + (i+1) + "个参数的值为：" + arguments[i] + "<br>";
                                                }
                                                return str;
                                        }
                                        else
                                        {
                                                var z = x * y;
                                                return z;
                                        }
                                }
                                document.write(myFun(2,4,8) + "<br>");
                                document.write(myFun(2) + "<br>");
                                document.write(myFun(2,4) + "<br>");
                        -->
                </script>

+=:赋值
比如:x+=y等于x=x+y

哦。那谢谢了哈。

多讲一句，其实x+=y并不完全等同于x=x+y，具体我也说不太清

……
ls的很异想天开啊，两者就是相等的～～～～
去看任何语言转换后的汇编代码或二进制代码就知道了。

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