Get position in textarea field

Question

I'm trying to get the cursor position inside a textarea in order to handle a custom wysiwig editor I'm building.

It's working correctly except for one thing. When no text is selected, right now I'm adding the BBCODE at the end of the current input. I would rather like to insert that BBCODE in the current cursor position.

This is what I have right now

function loadEditor(){
    var input = document.getElementById('editor-content');
    var btnBold = document.getElementById('bold');
    var blur = null;

    var clearSelect = function() {
      input.setSelectionRange(0, 0);
    };

    input.addEventListener('blur', function() {
        blur = setTimeout(clearSelect, 0);
      });

    btnBold.addEventListener('focus', function() {
      if (blur !== null) {
        clearTimeout(blur);
        blur = null;
      }
    });

    btnBold.addEventListener('click', function() {
        var openCode = "[b]";
        var closeCode = "[/b]";
        var emptyValue = openCode + closeCode;
        var fullText = input.value;
        var selected = input.value.substring(input.selectionStart, input.selectionEnd);
        if(selected == ""){
            input.value = input.value + emptyValue
        }else{
            input.value = input.value.replace(selected,openCode+selected+closeCode);
        }
        clearSelect();
    });
}

Thanks for your assistance