Simple ajax form submit

gistfile1.js

//right inside of your window.onload function

var formButton = document.querySelector('the_id_of_your_forms_button_here');

formButton.addEventListener('click', function(e){
  //stop form from submitting through the browser the default way
  e.preventDefault();
  
  var name = document.querySelector('id_of_the_name_field').value;
  var address = document.querySelector('id_of_the_address_field').value;
  //and so on until you've gotten all the values from the form
  
  var newLi = document.createElement('LI');
  //do what you did in your loop before to add the right elements and information to the new li
  var list = document.querySelector('id_of_the_list');
  
  list.appendChild(newLi);
  
  //send data to server with POST
  var req = new XMLHttpRequest();
  req.open("post", '/contacts', true);
  req.setRequestHeader("Content-Type", "application/json;charset=UTF-8");
  req.send(JSON.stringify({name: name, 
    addres: adress //and so on
  }));
  
  //clear out the form here
  
});