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mini-coi

This project ensures your browser's complicated Cross Origin Isolation (COI) settings "just work"™ for web workers. This is especially useful when you have no control over the HTTP headers returned by the server.

The simplest way to use mini-coi is to place the mini-coi.js file in the root of your website (i.e. /), and reference it as the first child tag in the <head> of your HTML documents:

<script src="/mini-coi.js" scope="./"></script>

For more complete technical details, read on...

What is mini-coi?

A minimalistic CLI utility or a simplified version of coi-serviceworker, with an optional scope attribute to define where Cross Origin Isolation should happen.

CLI

Bootstrap a local server with all headers enforced:

npx mini-coi .

# the third argument is a path so ...
# npx mini-coi ./public/
# npx mini-coi ./test/
# ...

The CLI brings in what's possible already to do with static-handler by passing --coi by default.

Service Worker

Allow headers in places like GitHub pages or any other server where you cannot change current headers:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src="./mini-coi.js" scope="./"></script>
</head>
</html>

What's different from coi-serviceworker?

  • no options at all: "it just works" ™
  • always require-corp to have this working on Safari as well as Chrome or Firefox
  • errors are just thrown in devtools

How to use mini-coi as Service Worker

  • the file must be a local file, you can't use any CDN or raw GitHub URL, you need to copy the file content locally 1
  • the script must not be a module, it has to be exactly a <script src="./mini-coi.js"></script> at the top of your <head> tag in your page (or in general before any other script or link or style is used, it can be after meta and title though)

Footnotes

  1. You can either use the CLI utility:

    npx mini-coi -sw public/mini-coi.js

// or ...
npx mini-coi --service-worker public/mini-coi.js

    Or you can grab the file from a CDN and save it locally:

    # grab mini-coi.js and save it locally as mini-coi.js
curl -LO https://raw.githubusercontent.com/WebReflection/mini-coi/main/mini-coi.js
    ↩