Lint docs js too and use `strict consistently. (#24160)

docs/4.0/components/forms.md

@@ -739,18 +739,19 @@ When attempting to submit, you'll see the `:invalid` and `:valid` styles applied
 <script>
 // Example starter JavaScript for disabling form submissions if there are invalid fields
 (function() {
-  "use strict";
-  window.addEventListener("load", function() {
-    var form = document.getElementById("needs-validation");
-    form.addEventListener("submit", function(event) {
-      if (form.checkValidity() == false) {
+  'use strict';
+
+  window.addEventListener('load', function() {
+    var form = document.getElementById('needs-validation');
+    form.addEventListener('submit', function(event) {
+      if (form.checkValidity() === false) {
         event.preventDefault();
         event.stopPropagation();
       }
-      form.classList.add("was-validated");
+      form.classList.add('was-validated');
     }, false);
   }, false);
-}());
+})();
 </script>
 {% endexample %}