JS: Collect a one-off keyboard response, using JQuery namespaces to allow multiple, overlapping responses

collect_keyboard_resp.js

/* collect a one-off keyboard response, using JQuery namespaces to allow multiple, overlapping responses
 *   fcn(e): function to be called with event on key press
 *   keys:   vector of allowed keys (as characters, uppercase for alphanumeric) (optional)
 *   to:     timeout for response, in ms (optinal)
 *   tofcn:  function to be called on timeout (optional)
 */

function collect_keyboard_resp(fcn, keys, to, tofcn) {
    // create unique namespace for this response
    var namespace = '._resp' + (new Date()).getTime();

    // bind keyup handler
    $(document).bind('keyup' + namespace, function(e) {
        // filter key-presses by list of allowed keys, if present
        if (!keys || keys.indexOf(String.fromCharCode(e.which)) != -1) {
            $(document).unbind(namespace);
            fcn(e);
            e.stopImmediatePropagation();
            return false;
        } else {
            return true;
        }
    });

    // if timeout function is specified, create event for calling it asynchronously
    if (typeof tofcn !== 'undefined') {
        $(document).bind('to' + namespace, function() {
                             $(document).unbind(namespace);
                             tofcn();
                         });
    }

    // if timeout is specified, set all handlers (keyup as well as timeout event) to expire
    if (typeof to !== 'undefined') {
        // timeout response after specified time and call function if it exists
        setTimeout(function(e) {
                       $(document).trigger('to' + namespace);
                       $(document).unbind(namespace);
                   }, to);
    }
}