post.js

function shirtIt(name) {
  var xhr = new XMLHttpRequest();
  xhr.onload = function (e) {
    if (xhr.readyState === 4) {
      if (xhr.status === 200) {
        alert(JSON.parse(xhr.responseText));
      }
    }
  };
  xhr.open('POST', '/'+name+, true);
  xhr.setRequestHeader('Content-Type', 'application/json; charset=UTF-8');
  xhr.send(data);
}

document.getElementById('button').addEventListener('click', function() {
  var name = document.getElementById('name');
  shirtIt(name);
}, false);