javascript - detect ctrl key pressed or up, keypress event doesn't trigger

I see some similar questions here (like JavaScript: Check if CTRL button was pressed) but my problem is actually the event triggering. My js code:

    // Listen to keyboard. 
    window.onkeypress = listenToTheKey;
    window.onkeyup = listenToKeyUp;

    /*
        Gets the key pressed and send a request to the associated function
        @input key
    */
    function listenToTheKey(e)
    {
        if (editFlag == 0)
        {
            // If delete key is pressed calls delete
            if (e.keyCode == 46)
                deleteNode();

            // If insert key is pressed calls add blank
            if (e.keyCode == 45)
                createBlank();

            if (e.keyCode == 17)
                ctrlFlag = 1;
        }
    }

The event triggers for any other keys except the ctrl.
I need to also trigger it for ctrl.
I can't use jQuery/prototype/whatever so those solutions are not acceptable.

So... how can I detect the ctrl?

Try using if (e.ctrlKey).

MDN: event.ctrlKey