js knockout hotkey

/**
 * Examples: 
 * - hotkey: 'ctrl+5' -> when control and 5 are pressed the binding element either is clicked or focus (input, select, textarea, .hotkey-focus)
 * - hotkey: {trigger: 'shift+b} => same as above but with shift and b
 * - hotkey: 'ctrl+shift+5' -> same as above but also with shift
 * - hotkey: {trigger: obsHotKey, action: function(element)} => A trigger or action can be an observable as well. action takes a function. If a non function 
 * is passed in then the default focus or click event is fired
 * */

ko.bindingHandlers.hotkey = {
    init: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
        var options = ko.utils.unwrapObservable(valueAccessor());

        if (typeof options === "object") {
            var trigger = ko.utils.unwrapObservable(options.trigger.toLowerCase());
            var action = ko.utils.unwrapObservable(options.action);
        } else {
            var trigger = options;
        }

        var shift = trigger.indexOf("shift") > -1;
        var ctrl = trigger.indexOf("ctrl") > -1;
        var alt = trigger.indexOf("alt") > -1;
        var key = trigger.substring(trigger.length - 1);


        $(document).on("keydown", function (e) {

            if (e.shiftKey === shift && e.ctrlKey === ctrl && e.altKey === alt && e.which === key.toUpperCase().charCodeAt(0)) {

                // hot key hit
                if ($(element).hasClass("hotkey-pressed") === true) return;
                $(element).addClass("hotkey-pressed");

                if (action && typeof action === "function") {
                    action(element);
                } else {
                    //if a input select or textarea lets focus on it
                    if (element.tagName.toLowerCase() == "input"
                        || element.tagName.toLowerCase() == "textarea"
                        || element.tagName.toLowerCase() == "select")
                        $(element).focus();
                    else
                        $(element).click();
                }
                e.preventDefault();
            }

        });
        //to keep from continuing calling of the hot key
        $(document).on("keyup", function (e) {
            $(element).removeClass("hotkey-pressed");
        });
    }
};