ajax.js

// Ajax mode: abort
// usage: $.ajax({ mode: "abort"[, port: "uniqueport"]});
// if mode:"abort" is used, the previous request on that port (port can be undefined) is aborted via XMLHttpRequest.abort()

var pendingRequests = {},
	ajax;

// Use a prefilter if available (1.5+)
if ( $.ajaxPrefilter ) {
	$.ajaxPrefilter( function( settings, _, xhr ) {
		var port = settings.port;
		if ( settings.mode === "abort" ) {
			if ( pendingRequests[ port ] ) {
				pendingRequests[ port ].abort();
			}
			pendingRequests[ port ] = xhr;
		}
	} );
} else {

	// Proxy ajax
	ajax = $.ajax;
	$.ajax = function( settings ) {
		var mode = ( "mode" in settings ? settings : $.ajaxSettings ).mode,
			port = ( "port" in settings ? settings : $.ajaxSettings ).port;
		if ( mode === "abort" ) {
			if ( pendingRequests[ port ] ) {
				pendingRequests[ port ].abort();
			}
			pendingRequests[ port ] = ajax.apply( this, arguments );
			return pendingRequests[ port ];
		}
		return ajax.apply( this, arguments );
	};
}