Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end users experience

$.ajax({
		      url: "../serverpage.php",
		      type: "POST",
		      async: false, 
		      cache: false,
		      data: $('form').serialize(),
		      success : function(val){
                if(val =="success") {
			   alert("successfully!");
                }        
		      }
		    });

The reason for this warning is you must be using an XMLHttpRequest synchronous request (async:false) instead of asynchronous. So the user will have to wait until a response is received for the request sent to the server, thus if the request takes too long to process the user will have to wait, this leads to bad user experience, hence you must use async:true in the $.ajax call in jQuery/javaScript.