如何对数组的每个元素运行Ajax调用？

我用Ajax调用服务器返回了一个json字符串，该字符串被转换为js数组。现在我想对数组的每个元素运行Ajax调用。

例如，第一次Ajax调用返回学期1、2、3、4。现在我想检索第一学期的主题并在表中显示它们，然后检索第二学期的主题，并在表中显示所有的主题等等…….

我写了一个代码，但它显示了最后一个表中的所有主题。有人能帮我解决这个问题吗？

$.ajax(
       {
           type: "POST",
           url: "returnSemesterNumbers",
           data: "programId="+selectedprog,
           success: function(data)
           {
                var semesters=$.parseJSON(data);
                for(x in semesters)
                {
                    semnum=semesters[x].semesterNumber;
                    alert(semnum);
                    $("#tables").append('<table id=table'+x+' style=float:left><tr><td>'+semnum+'</td></tr>');
                    $.ajax(
                           {
                               type: "POST",
                               url: "returnCourses",
                               data: "programId="+selectedprog+"&semNum="+semnum,
                               success: function(data1)
                               {
                                   var courses=$.parseJSON(data1);
                                    for(y in courses)
                                    {
                                        $("#table"+x).append('<tr><td>'+courses[y].title+'</td></tr>');
                                    }
                               }
                             });
                    $("#table"+x).append('</table>');
                    }
               }
             });
            }
            else
            {
                $("#tables").css('display','none');
            }
});

The callback in your inner ajax call captures the x variable by reference.

Since all of the callbacks run after the loop, they all get the current value of x, which is the last element in the set.

You need to move the code in the loop into a separate function that takes x as a parameter.

The scope of variable x might also cause issues.

Instead of:

for(x in semesters)

try:

for(var x in semesters)

Which will declare x as a variable in the scope of your first success ajax function, rather than as a global that can be changed by any other code (including jQuery).