ServiceWorker-Demo makes use of two browser APIs to offer client-side page persistence for Oracle APEX applications:

1. ServiceWorker allows Javascript files to run as "service workers" - background processes that can intercept network requests and offer an alternative to the browser cache. We use this to save static resources, like the page HTML, CSS, and JS.

2. IndexedDB is a transaction-based client-side database that can store arbitrary Javascript objects. We use IndexedDB here to store form and form field data from the page. By default, we update our IndexedDB on change events and at fixed intervals. On page load, form field data is reset to its default values; we offer the option either continue, discarding the saved IndexedDB data, or to restore form field from the IndexedDB.

Note that regions and items that the client hasn't loaded yet will not work offline. This includes items that open a popup window, pages that source data from SQL queries, and pages that the browser has not previously seen before going offline. Because of way that APEX stores session state data in the URL, it's difficult to determine which pages to be cached in advance. If possible, limit offline availability to a single page that doesn't pull data from the server after page load.

HTTPS / TLS / SSL must be enabled for ServiceWorker to work - the ServiceWorker standard requires that pages that serve a ServiceWorker must have a secure origin.

sw.js must be placed in the ROOT webapp if Oracle Rest Data Services is configured to run as a servlet under Apache Tomcat. This is a security restriction imposed by the ServiceWorker standard - the scope of the ServiceWorker must be higher or equal to the page location.

Effectively, this means that if the page is served at example.com/ords/f?p=123:345, then sw.js must be served at example.com/sw.js or example.com/ords/sw.js.

On the filesystem, this looks like $CATALINA_HOME/webapps/ROOT/sw.js if the file is to be served at example.com/sw.js.
It might be possible to use URL remapping within Tomcat such that a static file could be served under example.com/ords/ - investigate further?

All other javascript files - those under the js directory - can be either served under the filesystem or uploaded as a shared component for the applicaiton.

To serve under the filesystem, drop the js folder into the ROOT webapp.

Or, upload other files individually under Applicaiton X > Shared Components > Static Application Files.

All Javascript files must be referenced on the page(s) where ServiceWorker and IndexedDB functionality is required.

The easiest way to do this is under the File URLs section on each page - one line per file.

• For files on the filesystem, use these:

../js/main.js
../js/db.js
../js/networkTest.js
../sw.js

• For files uploaded as shared components, use these:

#APP_IMAGES#/main.js
#APP_IMAGES#/db.js
#APP_IMAGES#/networkTest.js
../sw.js

ServiceWorker will automatically cache and serve pages without human intervention, but IndexedDB requires some work for integration with APEX.

At a minimum, the page needs

1. an inline dialog region that displays on page load, prompting the user to load or discard locally-saved changes.
2. A save button/status indicator that forces all fields on the page to be saved.
3. A Region Change dynamic action that saves an individual field on focus out.

main.js will, on page load, attempt to determine if there's a discrepancy between the input fields on the page and the saved values in IndexedDB; if there is, a modal dialog prompts the user to either restore or discard the changes.

The dialog region should have a static ID set under the Advanced section of its region properties. The same static ID should be set in the _MODAL_DIALOG variable in the main.js file.

The dialog should have two buttons: one to load values from IndexedDB, and another to discard values from IndexedDB. They should have dynamic actions attached that execute APEX_LOADALL() and APEX_DISCARDALL() as Javascript, respectively. It doesn't seem to matter what the affected elements for these actions are.

The status indicator should have a dynamic action that executes APEX_SAVEALL() as Javascript upon click. It should have a static ID set; set the corresponding static ID in [[[config_file]]].

The Region Change dynamic action should fire when any input field within the region is changed(usually, when one clicks away from a field).

The event should fire upon a Change of a Region, most likely the content region. The associated action should affect only the event source; it should execute APEX_SAVEFIELD(this) as Javascript.

Sometimes the ServiceWorker may keep caching an old version of a file or the IndexedDB may index the wrong values, particularly when the source for each of these are changed.

In production, increment the version numbers in sw.js and db.js to force the scripts to drop previous versions.

In development, unregister the current ServiceWorker and purge the cache and local storage through Developer Tools > Application > Clear Storage - check all of the boxes before selecting Clear Site Data.