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What are service workers?

How service workers work

A Service Worker is a background script that runs separately from the main browser thread. It allows features like push notifications, offline experiences, and background syncs. When a user subscribes to Web Push, the service worker is downloaded and persists even when they navigate away—enabling push notifications at any time.

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Migrating from another push provider

If you are switching providers, review our guide: Migrating to OneSignal from another service

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How to integrate OneSignal’s service worker

The OneSignal Service Worker files get added automatically through our plugins, and you should not add these files to your site manually. Return to Web push setup.

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Download the .js file

Download the OneSignalSDKWorker.js file from the OneSignal dashboard or Download the OneSignal Service Worker File here.

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Upload the .js file to your server

Our SDK defaults to looking in your site’s root for the OneSignalSDKWorker.js file, for example: https://yoursite.com/OneSignalSDKWorker.js You can simply upload this file to the root directory of your site and return to the Web push setup guide for next steps. However, it is recommended to place this OneSignalSDKWorker.js file in a subdirectory path that you will never link users to like https://yoursite.com/push/onesignal/OneSignalSDKWorker.js. You can place this file in the root, but it may conflict with other Service Workers you have now or may add in the future. Also, the file should be put in a permanent location path that will never change. Once a Service Worker is registered with the browser, it is difficult to change.

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Service Worker configuration

You now need to tell OneSignal where to find the Service Worker and set the registration scope. By default, the OneSignal SDK sets this to be the root of your site. If you placed the OneSignalSDKWorker.js file in your site’s root like https://yoursite.com/OneSignalSDKWorker.js then no further action needed. However, it is recommended to place the Service Worker file in a subdirectory with a registration scope that will never be used, like /push/onesignal/. The OneSignal service worker file OneSignalSDKWorker.js must meet these requirements:
  • The file must be publicly accessible, meaning you should be able to navigate to the file in a browser and see the code.
  • The file must be served with a content-type of application/javascript; charset=utf-8.
  • The file must point to the same site origin (your site domain). Pointing to a Service Worker on a different origin is not allowed. No CDNs or subdomains.

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Typical site setup - Service Worker configuration

In the OneSignal dashboard, go to your App’s Settings > Push Platforms > WebIn the Advanced section, toggle the Customize service workers paths and filenames switch and input your data.

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Path to service worker files

The directory to where the OneSignal Service Workers file will be available. If the Service Worker is available at: https://yoursite.com/push/onesignal/OneSignalSDKWorker.js then the path is: /push/onesignal/

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Main and Updater service worker filename

The .js filename, which contains the OneSignal importScripts line. If you did not change the file name, this will be: OneSignalSDKWorker.jsIf your server forces files to have lowercase, you can set the filename to be onesignalsdkworker.js

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Service worker registration scope

The path on the domain the Service Worker has control of. This should be a path that you will never link users to and never host any pages from now or in the future. A common path example: /push/onesignal/ and scope could be the same path or deeper like: /push/onesignal/js/

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OneSignal Service Worker migration guide

Follow this section only if you already use OneSignal, have a large amount of web push subscribers, and you want to change OneSignal’s Service Worker settings.
This guide is only for customers that use OneSignal on their website currently and want to move the OneSignalSDKWorker.js file to a different path or scope.
Migration steps for the OneSignalSDKWorker.js file (click to expand) OneSignal’s Service Worker defaults to a root scope which may create the following issues for your site:
  • Conflict with a PWA
  • Conflict with an AMP setup
  • Conflict with your caching Service Worker, or any other Service Worker feature that requires root scope
  • Your site has security requirements that do not allow third-party Service Worker code to run on a scope that controls a page your users will visit.
If one or more apply to you then please follow the this guide.

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Picking a OneSignal Service Worker Scope

It is recommended you pick a Service Worker scope path you will never link a user to, but is still clear what it does. Example: /push/onesignal/. This way your PWA, AMP, or any other caching ServiceWorker can control the page a user views to work correctly. It is ok to put multiple service workers in the same location path, but MUST have unique scope path.

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Safely change the OneSignal Service Worker Scope

It is recommend to only change the scope if possible, changing the filename or location path of the Service Worker itself has additional considerations. Pay close attention to both the details of which scenario applies to you as well as each step to ensure you don’t lose subscribers or run into notification display issues

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Setup Type 1. Default OneSignal Setup - Scope root “/” AND default OneSignalSDKWorker.js Contents

Confirm the contents of your OneSignalSDKWorker.js file is the same as found in Download the OneSignal Service Worker File here. (Without any other non-OneSignal code you may need in it)In this case you can change the OneSignal scope to anything you choose to make room for another Service Worker to be placed at the root scope. See above Customize Your Service Worker Integration.
If your OneSignalSDKWorker.js is not hosted on root of your domain today, example you do NOT have it hosted like this: https://mysite.com/OneSignalSDKWorker.js then you MUST keep hosting it with the Service-Worker-Allowed header for an extended period of time. (1 year or more is recommended)If possible we recommend adding a comment in your backend code or your internal documentation to ensure it doesn’t get accidentally removed.

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Setup Type 2. Uncommon - Scope root “/” AND OneSignalSDKWorker.js (or your configured filename) contains OneSignal + other code or importScripts

This is less common but you may have already done this by following this OneSignal guide “Integrating Multiple Service Workers”. If this setup still meets all your requirements highly recommend keeping your setup as is due to the complex and two phase roll out required break up the merged ServiceWorker file that handles push events.
This section applies if you have OneSignal AND either some other custom code or importScript like the following in in your current Service Worker.
importScripts("https://cdn.onesignal.com/sdks/web/v16/OneSignalSDK.sw.js");
//And some other site specific code in the same file example.
importScripts("https://site.com/my-other-service-worker.js");
1

Keep your existing service worker code.

Add a code comment to your existing ServiceWorker file above this line importScripts("https://cdn.onesignal.com/sdks/web/v16/OneSignalSDK.sw.js"); to keep it for a extended period of time. (a year or more is recommend, depends on how long you want to keep sending pushes to users who never re-visit your site). Example: // KEEP Until YYYY-MM-DD: Required for pushes to work correctly for users who have not re-visited to migrate to the new OneSignal specific ServiceWorker.
2

Create a new service worker file

Create a new OneSignalSDKWorker.js under a different directory, such as /push/onesignal/ with the following single line of code importScripts("https://cdn.onesignal.com/sdks/web/v16/OneSignalSDK.sw.js");
3

Follow the guide on “Customizing Your Service Worker Integration” to change your scope and filename and path.

4

At this point new and returning users will automatically be subscribed to the new OneSignal ServiceWorker.

5

Wait the amount of time (a year or so) as noted in step 1.

6

Follow the OneSignal - “Delete Users” guide to delete users older than the timeline you picked.

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Remove comment from original service worker

Lastly finally remove the importScripts("https://cdn.onesignal.com/sdks/web/v16/OneSignalSDK.sw.js"); line with the comment from your original root ServiceWorker.

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Migrating OneSignal ServiceWorker scope - FAQ

Why must I keep hosting the original ServiceWorker file URL if I change the name or location path?
This is required for those users who have not re-visited your site for the new filename to be picked up. The original ServiceWorker file will be fetched by the browser each time you send a push (if past cache expire time, max cache is 24 hours). You will see a spike in 404 errors returned from your hosting provider when sending a push if the original ServiceWorker file isn’t available. This may result more requests to your server. This also means those users won’t be getting the new OneSignal features and fixes.