A function that duplicates submit inputs as hidden inputs, for browsers that don't include the submit name/value when form.submit() is called

submit-surrogate.js

// Some browsers don't include the submit button's value when form.submit() is
// called. This function creates a click listener that duplicates a form's submit
// button as a hidden field so its name/value can be included in AJAX POSTs,
// allowing different processing based on different submit buttons.

// The only argument is a selector that represents the form you want to bind, 
// such as '#login-form'.

// Copyright © 2015 Jason Sylvester. MIT License:
// http://opensource.org/licenses/MIT

function submitSurrogate(formSelector) {
  var form = document.querySelector(formSelector);

  form.addEventListener('click', function (e) {
    var input = document.createElement('input'),
        previousActions = form.querySelectorAll('input[type="hidden"].submit-surrogate');

    for ( var i = 0; i < previousActions.length; i++ ) {
      form.removeChild(previousActions[i]);
    }

    if ( e.target.type && e.target.type.toLowerCase() === 'submit' ) {
      input.name = e.target.name;
      input.type = 'hidden';
      input.value = e.target.value;
      input.className = 'submit-surrogate';

      form.appendChild(input);
    }
  });
}