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javascript - ①$("#userName")[0]中的这个【0】表示什么意思呀？

WBOY
Release： 2016-06-06 20:15:58
Original
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<code>function check_form(){
    usernameObj = $("#userName")[0];
        //window.alert(usernameObj.value); //show usernameObj=[object HTMLInputElement]
    var language = $("#choose_language").val();
    if(usernameObj.value==''){
        showWarningMsg("<?php echo $L['enter_you_user_name']; ?>");
        return false;
    }
    pwdObj = $("#password")[0];
    if(pwdObj.value==''){
        showWarningMsg("<?php echo $L['enter_you_user_password']; ?>");
        return false;
    }
    var yanzheng = $("#user_varify").val();
    if(yanzheng==""&&yanzheng.length!=4){
        showWarningMsg("<?php echo $L['enter_you_user_yz']; ?>");
        return false;
    }
    requestUrl = formatAjaxUrl("std-index.php");
    $.post(requestUrl, {"language":language,"action":"login_in","username":usernameObj.value, 
                        "password": hex_md5(pwdObj.value)+"<?php echo $_SESSION["salt"]; ?>", 
                        "choose": document.getElementById("checkednames").value, 
                        "remember": "0","yanzheng":yanzheng},
             function(data, textStatus)  
            {  
        if (textStatus=="success") {
            errorCode = getErrorCode(data);
            switch (errorCode) {
                  case 0:
                      window.location = "<?php echo HOME_URL; ?>";
                      break;
                  case 1: 
                  case 2:
                      showWarningMsg("<?php echo $L['user_password_not_match']; ?>");
                      break;
                  case 3:
                      showWarningMsg("<?php echo $L['MSG_ERROR_LOCK']; ?>");
                      break;
                  case 4:
                      userHasLogin("<?php echo $L['MSG_ERROR_RELOGIN']; ?>");
                      break;
                case 5:
                      showWarningMsg("<?php echo $L['user_yz_not_match']; ?>");
                      refresh_img();
                      break;
                  case 6:
                      showWarningMsg("<?php echo $L['user_yz_outtime_login_agin']; ?>");
                      refresh_img();
                      break;
                  case 9: 
                      break;    
                  case 10: // admin & license doesn't exist
                      window.location = "i2/wizard/wiz_license.php";
                      break;
                  case 11: // admin & notice something
                      window.location = "i2/wizard/wiz_notice.php";
                      break;
                  case 12: // non-admin user & license doesn't exist
                      showWarningMsg("<?php echo $L['SW_LICENSE_UNREGISTER']; ?>");
                      break;
                  case 13: // non-admin & trial license expired
                      showWarningMsg("<?php echo $L['SW_LICENSE_EXPIRED']; ?>");
                      break;
                  case 20: // upgrade database fail
                      errorMsg = getErrorMsg(data);
                      showWarningMsg("<?php echo $L['MSG_ERROR_DB_CHECK_FAIL']; ?>" + errorMsg);
                      break;
                  case 99: 
                      errorMsg = getErrorMsg(data);
                      showWarningMsg( errorMsg );
                      break;
              }
        }
    }); 
    return false;
}</code>
Copy after login
Copy after login

①$("#userName")[0]中的这个【0】表示什么意思呀？
②函数最后加了一个return false；它的作用是什么呢？能否省略？
请大神赐教！

回复内容：

<code>function check_form(){
    usernameObj = $("#userName")[0];
        //window.alert(usernameObj.value); //show usernameObj=[object HTMLInputElement]
    var language = $("#choose_language").val();
    if(usernameObj.value==''){
        showWarningMsg("<?php echo $L['enter_you_user_name']; ?>");
        return false;
    }
    pwdObj = $("#password")[0];
    if(pwdObj.value==''){
        showWarningMsg("<?php echo $L['enter_you_user_password']; ?>");
        return false;
    }
    var yanzheng = $("#user_varify").val();
    if(yanzheng==""&&yanzheng.length!=4){
        showWarningMsg("<?php echo $L['enter_you_user_yz']; ?>");
        return false;
    }
    requestUrl = formatAjaxUrl("std-index.php");
    $.post(requestUrl, {"language":language,"action":"login_in","username":usernameObj.value, 
                        "password": hex_md5(pwdObj.value)+"<?php echo $_SESSION["salt"]; ?>", 
                        "choose": document.getElementById("checkednames").value, 
                        "remember": "0","yanzheng":yanzheng},
             function(data, textStatus)  
            {  
        if (textStatus=="success") {
            errorCode = getErrorCode(data);
            switch (errorCode) {
                  case 0:
                      window.location = "<?php echo HOME_URL; ?>";
                      break;
                  case 1: 
                  case 2:
                      showWarningMsg("<?php echo $L['user_password_not_match']; ?>");
                      break;
                  case 3:
                      showWarningMsg("<?php echo $L['MSG_ERROR_LOCK']; ?>");
                      break;
                  case 4:
                      userHasLogin("<?php echo $L['MSG_ERROR_RELOGIN']; ?>");
                      break;
                case 5:
                      showWarningMsg("<?php echo $L['user_yz_not_match']; ?>");
                      refresh_img();
                      break;
                  case 6:
                      showWarningMsg("<?php echo $L['user_yz_outtime_login_agin']; ?>");
                      refresh_img();
                      break;
                  case 9: 
                      break;    
                  case 10: // admin & license doesn't exist
                      window.location = "i2/wizard/wiz_license.php";
                      break;
                  case 11: // admin & notice something
                      window.location = "i2/wizard/wiz_notice.php";
                      break;
                  case 12: // non-admin user & license doesn't exist
                      showWarningMsg("<?php echo $L['SW_LICENSE_UNREGISTER']; ?>");
                      break;
                  case 13: // non-admin & trial license expired
                      showWarningMsg("<?php echo $L['SW_LICENSE_EXPIRED']; ?>");
                      break;
                  case 20: // upgrade database fail
                      errorMsg = getErrorMsg(data);
                      showWarningMsg("<?php echo $L['MSG_ERROR_DB_CHECK_FAIL']; ?>" + errorMsg);
                      break;
                  case 99: 
                      errorMsg = getErrorMsg(data);
                      showWarningMsg( errorMsg );
                      break;
              }
        }
    }); 
    return false;
}</code>
Copy after login
Copy after login

①$("#userName")[0]中的这个【0】表示什么意思呀？
②函数最后加了一个return false；它的作用是什么呢？能否省略？
请大神赐教！

我能很喜感的说，菜鸟看菜鸟写的代码吗？
两句都是废话。
$('#userName')表示根据id查找对象，但是html规范中id是唯一的，所以这里的[0]虽然是得到了js原生对象，但是实际上一点用都没有，参考后面的
var yanzheng = $("#user_varify").val();
同样的

<code>usernameObj = $("#userName")[0];
if(usernameObj.value==''){
    showWarningMsg("<?php echo $L['enter_you_user_name']; ?>");
    return false;
}</code>
Copy after login

可以等效为

<code>usernameObj = $("#userName")[0];
if(! $("#userName").val().length){
    showWarningMsg("<?php echo $L['enter_you_user_name']; ?>");
    return false;
}</code>
Copy after login

结尾的return false用来阻止事件冒泡，但是源码中的onclick="check_form(); return false;"既然又写了一个return false，那么函数里面那个写不写都没用，反正没挂return。
正确的方式是


因为访问者按回车也会触发表单提交，这样不需要点击submit按钮从而绕过了检测。
再说这个方法最好命名为ajaxSubmit之类的名字，而不是checkform，因为里面包含了提交处理。

这段代码的整体逻辑是
当点击提交按钮的时候对form数据进行检查，如果检查成功使用ajax提交数据。return false是用来阻止form产生普通的表单提交。

明白意思就好了，代码本身没什么值得学习的。

1.选择这个是返回jquery对象。
2.是取消动作用的。

建议你重新看下犀牛书，毫无基础的样子。

把jq对象，转换成，原生js对象。此时你不能用jq的方法，只能用js的所支持的dom方法操作。你还可以使用$("#userName").get(0)获取原生js对象，但是建议用数组下标的方法，这种方法更快捷。

①$(selector)返回的是jQuery对象，$(selector)[0]是返回原生的DOM对象，即document.getElementById()返回的那种对象。（不明白这里代码为什么一会用jQuery的方式一会用原生DOM...）
②这个函数是submit form用的吗，如果是的话，return false;的作用是取消form的提交

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