# Using Service Workers with PageBuilder Engine

Source: https://dev.arcxp.com/pagebuilder-engine/core-concepts/using-service-workers-with-pagebuilder-engine/

PageBuilder Engine developers often want to adopt newer web platform features in their applications. This document covers [Service Workers](https://developer.mozilla.org/en-US/docs/Web/API/Service%5FWorker%5FAPI), which act as proxies between your apps and the external services they use.

> **Important:**
> 
> Before going live, contact Arc XP Customer Support (ACS) to request root-level JavaScript routing for service workers. If this is not enabled, requests to `/sw.js` will return a 404.

PageBuilder Engine includes behavior designed to support serving service worker scripts. Service worker scripts kept in the `resources` directory of your PageBuilder Engine feature pack are automatically stored and served directly from S3, speeding up the delivery of those script assets.

Additionally, we’ve set up the server to simplify the work needed to pull down those service worker scripts. If a request is made for a `.js` file from the root domain without an `outputType` query param (for example, `/sw.js`), PageBuilder Engine can serve the file from `resources/sw.js`.

This behavior is **not enabled by default**. It requires a root-level JavaScript rewrite to be enabled by the Arc XP Delivery team. Until that rewrite is enabled, requests to `/sw.js` will return a 404.

For a service worker script located at `resources/sw.js`, you can install and register it using: `navigator.serviceWorker.register('{deployment(/sw.js)}')` (the deployment ID must still be appended) and it will automatically get pulled down from S3\. Since all static resources are specific to a deployment, service worker scripts must also have a deploymentID param appended.

### Verifying root-level JavaScript routing

You can check whether root-level JavaScript routing is enabled for a site in Arc Admin.

1. Go to **Arc Admin**.
2. Open the **Delivery** tile.
3. Select the site you want to check.
4. Open the site detail page.
5. In the **Additional properties** section, look for `ROOT_JS_REWRITE`.
- `ROOT_JS_REWRITE = false` means root-level routing is disabled. This is the default.
- `ROOT_JS_REWRITE = true` means requests like `/sw.js` are rewritten to `resources/sw.js`.

If the property is false, contact Arc XP Customer Support to request it be enabled.

> **Note:**
> 
> This special rewrite//routing has only been created for files ending in `.js` without an `outputType` query param. No similar routing exists for other file types in `resources` folder.