Rewrite JS in ES5 compatible manner

modules/core/templates/loginuserpass.twig

@@ -38,7 +38,7 @@
     <p>{{ 'A service has requested you to authenticate yourself. Please enter your username and password in the form below.'|trans }}</p>
     <br>
     <div class="center">
-        <form class="pure-form pure-form-aligned center-form" action="{{ moduleURL('core/loginuserpass', {'AuthState': AuthState}) }}" method="post" name="f">
+        <form id="f" class="pure-form pure-form-aligned center-form" action="{{ moduleURL('core/loginuserpass', {'AuthState': AuthState}) }}" method="post" name="f">
             <div class="form-align">
 
                 <div class="pure-control-group">

modules/core/www/assets/js/loginuserpass.js

-$(document).ready(function () {
-    $('#submit_button').on('click', function () {
-        $(this).attr('disabled', 'disabled');
-        $(this).html($(this).data('processing'));
-        $(this).parents('form').submit();
-    });
+window.readyHandlers = [];
+window.ready = function ready(handler) {
+  window.readyHandlers.push(handler);
+  handleState();
+};
+
+window.handleState = function handleState () {
+  if (document.readyState === 'interactive' || document.readyState === "complete") {
+    while(window.readyHandlers.length > 0) {
+      (window.readyHandlers.shift())();
+    }
+  }
+};
+
+document.onreadystatechange = window.handleState;
+
+ready(function () {
+  // your code here
+  var button = document.getElementById("submit_button");
+  button.onclick = function () {
+      this.innerHTML = button.getAttribute("data-processing");;
+      this.disabled = true;
+
+      var form = document.getElementById("f");
+      form.submit();
+      return true;
+  };
 });