How do you structure an infinitely scalable form using Javascript?

<div id="product1"></div>
<div id="product2"></div>
<div id="product3"></div> etc...

document.getElementById('product').innerHTML += <input name="product">

$("someContainerDiv").insert(new Element("div", { id: "product_"+prodId, 'class':'prod' }))

output = '';
for(i in products){
   output += '<div id="product_' + products[i].id + '">';
   output += '<input type="text" name="products[' + products[i].id + '][name]">';
   output += '<input type="text" name="products[' + products[i].id + '][price]">';
   output += '</div>';
}
$('#products_list').append(output);