Toggle Contact Form fields with JavaScript

I want to toggle some fields depending on what the visitor chooses at this page http://ift.tt/1rF8gYS so I created a dropdown menu with the id puesto and the fields to toggle with the class condicional then I added this script

document.getElementById("puesto").onchange = CamposOcultos(document.getElementById("puesto").value);

function CamposOcultos(valor){
if (valor == "Modelo" or valor == "Promotor/a"){
for (var i=0;i<document.getElementsByClassName('condicional').length;i+=1){
  document.getElementsByClassName("condicional")[i].style.display="block";}
else{ 
for (var i=0;i<document.getElementsByClassName('condicional').length;i+=1){
  document.getElementsByClassName("condicional")[i].style.display="none";} }
}

But I get the following error when I try to load the function in the chrome console

Uncaught SyntaxError: Unexpected identifier(…)

Any idea how can I make it work ?

Thanks !

PS: I am using Contact Form 7 on WordPress

via Chebli Mohamed