As @dreta said there's only one way and it's by using a `keypress` event handler just like this:

    var keyInput = document.getElementById("keyInput");

    function inputFunc(e) {
        If (e.keyCode == 82) {// 82 = R
            //Do Something
        };
    };
    keyInput.addEventListener("keypress", inputFunc);

You can also visit this website where you can check the keyCode char
[keyCode char][1]


  [1]: http://www.cambiaresearch.com/articles/15/javascript-char-codes-key-codes