Features

Epos comes with a set of high-level features that are preconfigured to work across all execution contexts with no extra setup.

This page is a quick overview of some of them. Each feature has its own guide and API reference if you want the full details.

Messaging

epos.bus is the messaging layer for communication between the popup, background, side panel, web pages, and iframes.

It is like chrome.runtime.sendMessage, but much more powerful and easier to use.

// background.ts
epos.bus.on('user:get', async (userId: string) => {
  return await fetchUser(userId)
})

// popup.ts
const user = await epos.bus.send<User>('user:get', '42')

// content-script.ts
const user = await epos.bus.send<User>('user:get', '42')

You do not need to switch between different messaging APIs depending on the context or worry about routing. Epos handles that for you.

Shared State

epos.state gives you a shared object that is synchronized across contexts and persisted between sessions.

// Connect to a shared state
const state = await epos.state.connect()

// Use it like a normal object, changes are synced and persisted
state.count = 10
state.items = []
state.items.push('Hello')

In React, wrap components with epos.component() and they will update automatically when the state changes.

Read more in the State Management guide.

Storage

epos.storage is a persistent key-value store powered by IndexedDB.

await epos.storage.set('theme', 'dark')
const theme = await epos.storage.get<string>('theme')

It also supports files, blobs, and other binary data. It is available in all contexts, including web pages and iframes.

Extension APIs

epos.browser.* mirrors chrome.* APIs and makes them available in all contexts.

// content-script.ts
const tabs = await epos.browser.tabs.query({})

You are no longer limited to any context restrictions. Just use epos.browser and it will work everywhere.

Simple Setup

epos.json replaces manifest.json and lets you define your extension in a simpler way. You tell Epos which files to load and where, and it handles the rest.

json

{
  "name": "My Extension",
  "targets": [
    {
      "matches": "<popup>",
      "load": ["dist/popup.js"]
    },
    {
      "matches": "*://*.example.com/*",
      "load": ["dist/main.js", "dist/main.css"]
    }
  ]
}

Epos turns that configuration into a standard manifest.json during export.

Features ​

Messaging ​

Shared State ​

Storage ​