检查页面上是否有一些ajax正在处理中？

I have this code

我有这个代码

$('#postinput').on('keyup',function(){ 
    var txt=$(this).val();

    $.ajax({
       type: "POST",
       url: "action.php",
       data: 'txt='+txt,
       cache: false,
       context:this,
       success: function(html)
       {
           alert(html);
       }

   });

});


$('#postinput2').on('keyup',function(){ 
    var txt2=$(this).val();

    $.ajax({
       type: "POST",
       url: "action.php",
       data: 'txt2='+txt2,
       cache: false,
       context:this,
       success: function(html)
       {
           alert(html);
       }

   });

});
$('#postinput').on(