Terii is a tiny little library to help you manage state across your application. Terii creates a central store that enables you to both better control and cascade state across your application. The code and parts of the documentation have been taken from

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Terii is a tiny library to help you manage state across your application. It was originally written by Andy Bell under another name: Beedle.

I have ported Andy's code to TypeScript (and added unsubscribe). That's all folks.

Terii (japanese: テリー pron. Terī) is the japanese name of the character Beedle from The Legend of Zelda series. It might be better written as Terry, but it was not available on npm, 😅

Table of Contents

Getting started

You can pull Terii down via npm or take a zip of this repository. The rest of this guide assumes you've used npm.


npm install terii

Create a store instance

First up, import it into your JavaScript:

import { Store } from 'terii'

Once you've got that you should create some actions, mutations and some initial state:

const actions = {
  saySomething(context, payload) {
    context.commit('setMessage', payload)

const mutations = {
  setMessage(state, payload) {
    state.message = payload

    return state

const initialState = {
  message: 'Hello, world',

Once you've got those setup, you can create a Store instance like this:

const storeInstance = new Store({

Use in your app

Let's say you've got a text box that you type a message into. When the content is changed, it could dispatch a new message to your store:

// Grab the textarea and dispatch the action on 'input'
const textElement = document.querySelector('textarea')

textElement.addEventListener('input', () => {
  // Dispatch the action, which will subsequently pass this message to the mutation
  // which in turn, updates the store's state
  storeInstance.dispatch('saySomething', textElement.value.trim())

Listen for changes (and stop listening)

Terii uses the Pub/Sub pattern to transmit changes. Let's attach the message to a DOM element:

// Grab the text element and attach it to the stateChange event
const messageElement = document.querySelector('.js-message-element')

// This fires every time the state updates
storeInstance.subscribe('.js-message-element', (state) => {
  messageElement.innerText = state.message

If necessary, we can stop listening for changes by unsubscribing:

// we stop listening to what we subscribed earlier

How it works

Terii creates a pattern where a single source of truth, the 'Application State' cascades state across your app in a predictable fashion. To modify state, a set flow of actions and mutations help create a traceable data-flow that makes things a little easier to debug.

Using a Pub/Sub pattern which notifies anything that is subscribed to changes, a fully reactive front-end can be achieved with a few kilobytes of vanilla JavaScript.

A mini library for small projects

Terii is inspired by libraries like Redux, but certainly isn't designed to replace it. Terii is aimed more at tiny little applications or where a development team might be looking to create the smallest possible footprint with their JavaScript.

Performance budget

Terii is intended to be tiny, so the largest that the uncompressed size will ever get to is 5kb.

Browser support

Terii is aimed at browsers that support ES6 by default. It also uses a Proxy to monitor state, so anything that supports Proxy will support Terii.

You could use the Proxy polyfill to support more browsers.

Most major browsers will support Terii with no issues.


TypeScript types are included.


If you are intereseted in contributing to this project, please refer to the documentation.


Check the releases page for the latest changes.


Original work Copyright (c) 2018 Andy Bell - MIT License

Modified work Copyright (c) 2021 Mirco Sanguineti - See License