Focus on a textarea to the last + 1 character cursor, javascript

Question

I have this portion of code in my javascript file

function insertRespuesta(id, attach)
{
    document.getElementById(attach).value += " #" + id + " ";
    document.getElementById(attach).focus();
}

My html file:

<textarea name="textoConversacion" id="textoConversacion" class="mensaje-mensajeria"></textarea>
<a href='#' class='decoracion-link' onClick="insertRespuesta('<?php echo $cada['contador']; ?>','textoConversacion');">#<?php echo $cada['contador']; ?></a>

So if I click the link it will be focused on the textarea but the textarea cursor will be in the last position I had, and I need to put in the last cursor character + 1.

I preffer not using jquery.

Answer 1

From the linked answer which does not use jQuery:

function insertRespuesta(id, attach)
{
    var el = document.getElementById(attach)
    if(el != null)
    {
        el.value += " #" + id + " ";
        setCaretPosition(attach, el.value.length);
    }
}

function setCaretPosition(elemId, caretPos) {
    var elem = document.getElementById(elemId);

    if(elem != null) {
        elem.focus();
        if(elem.createTextRange) {
            var range = elem.createTextRange();
            range.move('character', caretPos);
            range.select();
        }
        else if(elem.selectionStart) {
            elem.setSelectionRange(caretPos, caretPos);
        }
    }
}

Here is a working jsFiddle.