createForm.js

var createForm = function(action, fields) {
  function isObject(val) {
    if (val === null) { return false;}
    return ( (typeof val === 'function') || (typeof val === 'object') );
  }

  if (!isObject(fields))
    return;

  // Create form
  var f = document.createElement('form');
  f.setAttribute('action', action);
  f.setAttribute('method', 'post');
  f.setAttribute('hidden', 'true');

  // Append form fields
  for (var k in fields)
  {
    var field = document.createElement('input');
    field.setAttribute('type', 'hidden');
    field.setAttribute('name', k);
    field.setAttribute('value', fields[k]);

    f.appendChild(field);
  }

  // Add form fields
  return f;
}