验证码的代码

<script type="text/javascript">
                                                var rndKey;
                                                function randomnum(num) {
                                                    var m = "";
                                                    for (var i = 0; i < num; i++)
                                                    { var n = Math.floor(Math.random() * 10); m += n; }  解释｛Math.random() * 6 生成0和6之间的随机小数，Math.floor(x)函数，返回小于等于x的最大整数｝
                                                     return m;
                                                 }
                                                 function GetKey() {
                                                     var key = randomnum(4);
                                                     rndKey = key;
                                                     document.getElementById("CheckImgKey").value = key;
                                                     document.getElementById("CheckImg").src = "Login/ImgKey.aspx?key=" + key;｛解释：SQJZ项目下的Login/ImgKey.aspx｝
                                                 }
 window.document.write("<input tabindex='3' name='UserKey' type='text' id='UserKey' class='input' size='5' style='width:95px;height:18px;' maxlength='4' /><input id='CheckImgKey' name='CheckImgKey' type='hidden' />");
 window.document.write(" <img id='CheckImg' align='absmiddle' src='images/ImgKey.jpg' style='width:50px;height:22px;cursor:pointer;' onclick='GetKey();' alt='点击换一个'>");
                                                 GetKey();
                                                 $(function() {
                                                 window.setTimeout("ResetKey()", 1000); });
                                                 function ResetKey() {
                                                     $("#CheckImgKey").attr("value", rndKey);
                                                 }
                                            </script>