Create HTML elements using an external Javascript file

Question

I am new to Javascript and would like to create elements dynamically using external Javascript file. However I am unsuccessful.

Follow the code below:

function add (){

    var texto = document.createTextNode("teste");
    var p = document.createElement("h1");
    var ptexto = p.appendChild(texto);
    var body = document.getElementsByTagName("body")[0];
    body.appendChild(ptexto);

}

I can’t add the elements to the body of the document.