我是JavaScript的新手，我无法理解一些脚本中的变量范围，我已经从我找到的示例拼凑起来了。下面的代码是Matt Berseth在他的网站上发布的教程的一部分。该应用程序有一个ajaxToolKit：ModalPopupExtender，带有JavaScript函数，可在单击Yes或No按钮时执行。应该保存删除按钮位置和div的两个变量似乎没有填充，因此代码异常。当我单击Yes或No按钮时，_Source和_popup变量都是未定义的。
我真的很感谢在我的代码中解释我设置错误的时间。
The button that is fires the OnClientClick event calling the SubmitPayment function
<asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClientClick="return SubmitPayment(this); return false;" UseSubmitBehavior="False" AccessKey="S" ValidationGroup="Manual" />
A hidden field to save a value in (tested later in the javascript)
<div id="divHiddenFields">
<asp:HiddenField ID="hfTotalAmtDue" runat="server" />
</div>
The Dialog Panel
<div id="divConfirmPaymentDialog">
//panel that makes up confirmation dialog
<asp:Panel ID="pnlConfirmPaymentDialog" runat="server" style="display:none" CssClass="modalPopup" Height="200" Width="450">
<div align="center">
<p class="info">You are attempting to make a payment when your account(s) has/have no balance!</p>
<p class="info">If you do this you will have a credit applied to your account in the amount of your payment.</p>
<p class="info">Are you sure that you want to do this?</p>
<asp:Button ID="btnConfirmPaymentYes" runat="server" Text="Yes" Width="75" />
<asp:Button ID="btnConfirmPaymentNo" runat="server" Text="No" Width="75" />
</div>
</asp:Panel>
//modal dialog extender that implements showing the modal dialog with panel
<cc1:ModalPopupExtender ID="mpeConfirmPayment" runat="server" BehaviorID="mpeConfirmPaymentBehaviorID" BackgroundCssClass="modalBackground"
CancelControlID="btnConfirmPaymentNo" OnCancelScript="btnConfirmPaymentNo_Click();" OkControlID="btnConfirmPaymentYes" OnOkScript="btnConfirmPaymentYes_Click();"
PopupControlID="pnlConfirmPaymentDialog" TargetControlID="pnlConfirmPaymentDialog" />
</div>
The Javascript
<script type="text/javascript">
//this system function sets the App_init handler function as the initialization handler
Sys.Application.add_init(App_Init);
//this function handles the hookup of the beginrequest and endrequest ="divhandlers. The two functions are called
//at the begin and end of the webpage lifecycle
function App_Init()
{
Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(BeginRequest);
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequest);
}
//this function handles the begining of the webpage lifecylce
function BeginRequest(sender, args){
$(document).ready(function(){
//if btnYes was clicked then block the UI
$('#<%= btnYes.ClientID %>').live('click', function(e){
//e.preventDefault();
$.blockUI();
});
});
}
//this function handles the end of the webpage lifecylce
function EndRequest(sender, args) {
//call unblockUI
$(document).ready(function() {
$('#<%= btnYes.ClientID %>').live('click', function(e) {
$.unblockUI();
});
});
//check for errors that occurred during page execution
if (args.get_error() != undefined) {
var errorMessage;
if (args.get_response().get_statusCode() == '200') {
errorMessage = args.get_error().message;
}
else {
// Error occurred somewhere other than the server page.
errorMessage = 'An unspecified error occurred. ';
}
args.set_errorHandled(true);
if (errorMessage.indexOf('ValidationError:') > 0) {
alert(errorMessage.replace('Sys.WebForms.PageRequestManager', '').replace('ServerErrorException:', ''));
}
}
}
//this funcion will raise the viewccreceipt dialog when called
function OpenReceipt() {
window.open('ViewCCReceipt.aspx', 'Name', 'height=600,width=800');
}
// keeps track of the delete button for the row
// that is going to be removed
var _source;
// keep track of the popup div
var _popup;
//This function will be called when the submit button on the creditcard entry screen is pressed.
//The function will check to see if the balance is already zero and message the customer that they will have a
//credit balance if they continue and allow the to confirm the payment.
function SubmitPayment(source) {
$(document).ready(function() {
//Get the Total Amount Due from hidden field hfTotalAmountDue
var TotalAmtDue = $('#<%= hfTotalAmtDue.ClientID %>').val();
if (TotalAmtDue <= 0) {
this._source = source;
this._popup = $find('mpeConfirmPaymentBehaviorID');
// find the confirm ModalPopup and show it
this._popup.show();
}
});
}
//event handler for the btnConfirmPaymentYes button
//when this handler is executed the modal popup is hidden and a postback is done
function btnConfirmPaymentYes_Click(){
// find the confirm ModalPopup and hide it
this._popup.hide();
// use the cached button as the postback source
__doPostBack(this._source.name, '');
}
//event handler for the btnConfirmPaymentNo button
//when this handler is executed the modal popup is hidden and the postback permanently shut down
function btnConfirmPaymentNo_Click(){
// find the confirm ModalPopup and hide it
this._popup.hide();
// clear the event source
this._source = null;
this._popup = null;
}
</script>
答案 0 :(得分：2)
this._source与JavaScript中的var _source不同。
而不是做
this._source = source;
this._popup = $find('mpeConfirmPaymentBehaviorID');
也许你应该做
_source = source;
_popup = $find('mpeConfirmPaymentBehaviorID');
将它（在文档加载时）分配给在包含事件处理函数定义的作用域中声明的变量：btnConfirmPayment{No,Yes}_Click。
很多时候两者是等价的，因为this默认引用全局范围，并且var声明在全局范围内，但在加载事件处理程序时可能运行{ {1}}是一些DOM节点。
答案 1 :(得分：1)
范围很棘手，这是基础知识。
唯一的范围是功能范围。函数中声明的变量保留在函数中。在函数外部声明的变量属于全局范围。但是要避免使用全局变量，因为它们的风格很差。
函数是没有home的对象。在两种情况下，您只能依赖this的值：
functionname.call(context, params)，其中context是this的值this将成为它的一部分
如果以这种方式调用函数：functionname(params)，那么this将是调用范围内的任何内容。这有点奇怪，所以如果你要使用它，请确保你知道它是什么。
您应该假设this永远不会引用全局范围，并且绝不应在全局范围内使用this。
我会使用某种打包器来避免使用全局范围。我使用ender.js，这很好，因为默认包与jQuery非常相似，所以学习曲线很小。
Douglas Crockford是解释JavaScript的人：