function add_field(addToo,type)
{
    switch(type)
    {
        case 'email':
            add_email(addToo);
            break;
    }
    // More case statements will be added later
}

function add_email(addToo)
{
    ++numEmail;
    var container = document.getElementById(addToo);
    // New parent DIV
    var div=document.createElement('div');
    div.id='email_'+numEmail;
    // New input text box
    var txt=document.createElement('input');
    txt.type='text';
    txt.name="email["+numEmail+"]";
    // Select box
    var sel=document.createElement('select');
    var opt1=document.createElement('option');
    var opt2=document.createElement('option');
    var opt3=document.createElement('option');
    sel.name='email_type['+numEmail+']';
    opt1.appendChild(document.createTextNode('Home'));
    opt2.appendChild(document.createTextNode('Work'));
    opt3.appendChild(document.createTextNode('Parent(s)'));
    opt1.value='Home';
    opt2.value='Work';
    opt3.value='Parents';
    sel.appendChild(opt1);
    sel.appendChild(opt2);
    sel.appendChild(opt3);
    // Remove link
    var a=document.createElement('a');
    a.setAttribute('href','#');
    a.setAttribute('onclick', "remove_node('email_"+numEmail+"'); return false;");
    a.appendChild(document.createTextNode('remove'));

    a.style.marginLeft='1.1em';

    div.appendChild(txt);
    div.appendChild(sel);
    div.appendChild(a);
    container.appendChild(div);
}


/*
 * Remove a child node from an HTML element.
 * id: the id of the node you wish removed from DOM.
 */
function remove_node(id)
{
    var elem=document.getElementById(id);
    elem.parentNode.removeChild(elem);
}



<p><a href="" onclick="add_field('emails','email');return false;">Add Email</a></p>
<div id="emails"></div>