https://www.pieddecochon.com/js/libs/jquery.validate.ajax.js?v=26

1// Ajax mode: abort
2// usage: $.ajax({ mode: "abort"[, port: "uniqueport"]});
3// if mode:"abort" is used, the previous request on that port (port can be undefined) is aborted via XMLHttpRequest.abort()
4
5var pendingRequests = {},
6	ajax;
7
8// Use a prefilter if available (1.5+)
9if ( $.ajaxPrefilter ) {
10	$.ajaxPrefilter( function( settings, _, xhr ) {
11		var port = settings.port;
12		if ( settings.mode === "abort" ) {
13			if ( pendingRequests[ port ] ) {
14				pendingRequests[ port ].abort();
15			}
16			pendingRequests[ port ] = xhr;
17		}
18	} );
19} else {
20
21	// Proxy ajax
22	ajax = $.ajax;
23	$.ajax = function( settings ) {
24		var mode = ( "mode" in settings ? settings : $.ajaxSettings ).mode,
25			port = ( "port" in settings ? settings : $.ajaxSettings ).port;
26		if ( mode === "abort" ) {
27			if ( pendingRequests[ port ] ) {
28				pendingRequests[ port ].abort();
29			}
30			pendingRequests[ port ] = ajax.apply( this, arguments );
31			return pendingRequests[ port ];
32		}
33		return ajax.apply( this, arguments );
34	};
35}