jquery.ui.autocomplete.cache.js

var initSource = $.ui.autocomplete.prototype._initSource;
$.ui.autocomplete.prototype._initSource = function() {
	if ( typeof this.options.source === "string" && this.options.cache ) {
		var self = this,
			cache = {};

		this.source = function( request, response ) {
			var term = request.term;
			if ( cache[ term ] ) {
				response( cache[ term ] );
				return;
			}
			self.xhr = $.getJSON( self.options.source, request, function( data, status, xhr ) {
				cache[ term ] = data;
				if ( xhr === self.xhr ) {
					response( data );
				}
			});
		};
	} else {
		initSource.call( this );
	}
};