app.js

var cambioTexto = document.body.childNodes[1];

document.getElementById('texto2').innerText = cambioTexto.innerText;

function mostrarTipoElementos(){
    var div = document.getElementsByTagName('div')[0];
    var tipos = "";

    for(var i = 0; i < div.childNodes.length; ++i){
        tipos += div.childNodes[i].nodeName + " ";
    }

    document.getElementsByTagName('p')[2].innerText = tipos;
}

function mostrarPrimerElemento(){
    document.getElementsByTagName('p')[2].innerText = document.getElementsByTagName('div')[0].firstChild.nextSibling.nodeName;
}

function mostrarUltimoElemento(){
    document.getElementsByTagName('p')[2].innerText = document.getElementsByTagName('div')[0].lastChild.previousSibling.nodeName;
}