为什么$ .ajax无法正常工作？

在我的网页中有一个文本框来获取扫描的条形码值，一旦我们扫描条形码，它必须从数据库获得详细信息。我正在为文本框创建更改事件，但遇到了一些问题。

问题：$.ajax不工作。

代码：

    var target = $('#txtBarcode'), val = target.val();
        target.change(monitor());
        function monitor() {
            $.ajax({
                type: "POST",
                contentType: "application/json; charset=utf-8",
                data: "{}",
                url: "HomePage.aspx/SearchProduct",
                dataType: "json",
                success: function(data) {
                alert("Success!!!");
                }
            });
        }
  1. Add an error handler.
  2. Make sure your relative URL is right.
 $.ajax({
            type: "POST",
            contentType: "application/json; charset=utf-8",
            data: "{}",
            url: "HomePage.aspx/SearchProduct",
            dataType: "json",
            success: function(data) {
            alert("Success!!!");
            },
            error: function(XMLHttpRequest, textStatus, errorThrown)
            {
              // ...
            }
        });

EDIT: Dan is right about your change handler.

You are trying to pass 'monitor' to the change method but you're actually calling it. It should look like this (no parens)

var target = $('#txtBarcode'), val = target.val();
        target.change(monitor);
        function monitor() {

You can always declare it inline too:

 var target = $('#txtBarcode'), val = target.val();
        target.change(
             function() {
                 $.ajax({
                  type: "POST",
                  contentType: "application/json; charset=utf-8",
                  data: "{}",
                  url: "HomePage.aspx/SearchProduct",
                  dataType: "json",
                  success: function(data) {
                             alert("Success!!!");
                           }
                 });
             });

You can copy some answers posted here, and at least one of will likely to work, but you won't get the intimate knowledge of why. Here's an additional way:

  1. Since you use asp.net, put the break point in the first line of HomePage.aspx/SearchProduct. This ensure that the request goes to the right URL on the server.

  2. Step all the way through this method to make sure there's no exception that gets thrown.

  3. Use FireFox and install Firebug (even if you target IE and have no intention to make it run on FF). You can inspect the http response.
  4. Add an error handler in addition to the success handler.