Código javascript
:
Ver originalvar fields = 1;
var agregar = function(fin){
fields++;
var n = document.createElement('input');
n.name = 'textfield'+fields, n.size = 15, n.type = "text", n.style.display = "block";
fin.parentNode.insertBefore(n,fin);
}
// Html
<form name="f1" id="f1" method="post" action="">
<input type="text" size="15" name="textfield1">
<input type="button" name="Submit" value="agregar" onclick="agregar(this)">
<input type="submit" name="Submit2" value="Enviar">
</form>