[Answer]-Stop an ajax call if it takes to much to complete

$.ajax({
    url: "test.html",
    error: function(){
        // will fire when timeout is reached
    },
    success: function(){
        //do something
    },
    timeout: 3000 // sets timeout to 3 seconds
});

From: Set timeout for ajax (jQuery)

Here is how to do it in jQuery

   $.ajax({
     type: "POST",
     url: "some.php",
     data: { name: "John", location: "Boston" }
     timeout: 4000 /*Miliseconds*/
   })
     .done(function( msg ) {
       alert( "Data Saved: " + msg );
     });

Vinilla JS i much more complex but the code you would end up with would be something like this

   xhr = new XMLHttpRequest();
   // ALOT OF OTHER CODE....
   xhr.timeout = 4000;