add navigate away prompt js utility

static/js/utils/form.js

@@ -247,6 +247,86 @@
     setup: interactiveFieldsetUtil,
   });
 
+  /**
+   *
+   * Navigate Away Prompt Utility
+   *  This utility asks the user if (s)he really wants to navigate away
+   *  from a page containing a form if (s)he already touched an input.
+   *  Form-Submits will not trigger the prompt.
+   *  Utility will ignore forms that contain auto submit elements (buttons, inputs).
+   *
+   * Attribute: [none]
+   *  (automatically setup on all form tags that dont automatically submit, see AutoSubmitButtonUtil)
+   *
+   * Example usage:
+   *  (any page with a form)
+   */
+
+  var NAVIGATE_AWAY_PROMPT_UTIL_NAME = 'navigateAwayPrompt';
+  var NAVIGATE_AWAY_PROMPT_UTIL_SELECTOR = 'form';
+
+  var NAVIGATE_AWAY_PROMPT_INITIALIZED_CLASS = 'navigate-away-prompt--initialized';
+
+  var navigateAwayPromptUtil = function(element) {
+    var touched = false;
+    var unloadDueToSubmit = false;
+
+    function init() {
+      if (!element) {
+        throw new Error('Navigate Away Prompt utility needs to be passed an element!');
+      }
+
+      if (element.classList.contains(NAVIGATE_AWAY_PROMPT_INITIALIZED_CLASS)) {
+        return false;
+      }
+
+      // ignore forms that get submitted automatically
+      if (element.querySelector(AUTO_SUBMIT_BUTTON_UTIL_SELECTOR) || element.querySelector(AUTO_SUBMIT_INPUT_UTIL_SELECTOR)) {
+        return false;
+      }
+
+      window.addEventListener('beforeunload', beforeUnloadHandler);
+
+      element.addEventListener('submit', function() {
+        unloadDueToSubmit = true;
+      });
+      element.addEventListener('change', function() {
+        touched = true;
+        unloadDueToSubmit = false;
+      });
+
+      // mark initialized
+      element.classList.add(NAVIGATE_AWAY_PROMPT_INITIALIZED_CLASS);
+
+      return {
+        name: NAVIGATE_AWAY_PROMPT_UTIL_NAME,
+        element: element,
+        destroy: function() {
+          window.removeEventListener('beforeunload', beforeUnloadHandler);
+        },
+      };
+    }
+
+    function beforeUnloadHandler(event) {
+      if (!touched || unloadDueToSubmit) {
+        return false;
+      }
+
+      // cancel the unload event. This is the standard to force the prompt to appear.
+      event.preventDefault();
+      // for all non standard compliant browsers we return a truthy value to activate the prompt.
+      return true;
+    }
+
+    return init();
+  };
+
+  formUtilities.push({
+    name: NAVIGATE_AWAY_PROMPT_UTIL_NAME,
+    selector: NAVIGATE_AWAY_PROMPT_UTIL_SELECTOR,
+    setup: navigateAwayPromptUtil,
+  });
+
   /**
    *
    * Auto Submit Button Utility