JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="foo">Some text</textarea>
<a href="#" onclick="insertRespuesta('id', 'foo');">link text</a>

JavaScript

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);
        }
    }
}