Vivisector | Convert any object into an evented, reactive state machine ✂️

API and Documentation

Table of Contents

• Introduction
  • Features
• Install
• Documentation
  • Getting Started
  • Event Types
  • Methods
  • State Commitment
• Next

Introduction

Convert any object into an evented, reactive state machine.

Vivisector is a light-weight building block for pub/sub modeling, state management, and reactive programming. Here, we may add event listeners to plain objects and arrays, binding N actions to their state mutations. Registered actions can then intercept state transitions and decide whether to commit or revert them.

const { vivisect } = require('vivisector-js');

const state = vivisect({
  firstName: '',
  lastName: '',
  email: ''
})
  .subscribe('set', ({ prevState, nextState, done }) => {
    if (!isValidEmail(nextState.email)) {
      emitErrorMessage();
      done(false);
    } else {
      sendWelcomeEmail();
      done(true);
    }

    ...
  });

Features

• 📦 zero dependencies
• 🪶 light-weight and compact at ~ 2kb gzipped
• 👌 simple and well-documented API
• 🔥 support for (and built with) TypeScript
• ✨ available for ESM, UMD, and CommonJS build targets
• 🚀 bind actions to a variable's state on the fly
• 🔌 harness the power of reactive programming without the excess boilerplate
• ✔️ preview, then declaratively cancel or commit state changes

Installation

Install via NPM

NPM:

npm install vivisector-js

Yarn:

yarn add vivisector-js

Documentation

Before we dive in, here's a couple of quick notes that are rather important:

• Vivisected objects are COPIED by value, not reference

• don't mutate state in callbacks - doing this will result in undefined behavior; that's what the done function is for

• nested objects become their own proxies

  For example, in the following code

  const o = vivisect({ a: {} });
  
  Object.assign(o.a, someObject);

  o.a will invoke events with a base state of {}

Getting Started

Let's manage some evented state!

First, we'll import the vivisect utility:

const { vivisect } = require('vivisector'); // assuming cjs for this tutorial, but Vivisector supports es modules, too

This function will take our object or array and return an evented copy.

In this example, we'll vivisect an array and register a callback function for the add event. Our callback will be invoked whenever new elements are added to the array. We'll keep things simple for now by passing along the alwaysCommit option, which means state transitions associated with add events will always be committed.

const logAdditions = ({ type, prevState, nextState }) => {
    console.log(`${type} event captured. ${prevState} --> ${nextState}`);
};

// instantiate our `users` list - what an interesting bunch!
const users = vivisect(['Damo Suzuki', 'Soren Kierkegaard', 'Donald Knuth']);

// every time an item is added to `users`, we want to invoke `logAdditions`
users.subscribe('add', logAdditions, { alwaysCommit: true });

// let's bring someone fictional into the mix
users.push('Elric of Melnibone');
// 'add event captured. ['Damo Suzuki', 'Soren Kierkegaard', 'Donald Knuth'] ==> ['Damo Suzuki', 'Soren Kierkegaard', 'Donald Knuth', 'Elric of Melnibone']

Both arrays and objects can be vivisected in this manner:

const albums = vivisect({ krautrock: ['Tago Mago', 'Monster Movie', 'Ege Bamyasi'] });

The object's prototype is unaffected, save for the added event registrars (more on these later)

console.log(Object.values(albums)[0].findIndex(i => i.startsWith('T')));; // 0

Event handlers are registered by calling subscribe. This method will exist on every vivisected object:

users.subscribe(eventType, eventHandler, options);

And when we're done, we can remove the handler by passing a reference to it into the unsubscribe method:

users.unsubscribe(eventType, eventHandlerRef);

Event Types

This section documents all builtin Vivisector events and their behaviors.

add

A new element or property has been added to the target. 'Add' typically constitutes as a new indexed property that previously did not exist.

Callbacks will receive a function, done, and an object consisting of:

Property	Value
type	Enum 'add', denoting the event-type that was triggered
prevState	the previous state
nextState	the next state, i.e. the result of the add event that was captured

Fires on: Additive array functions; adding new properties

Note: Operations such as Array.prototype.push are considered batched events if provided more than a single argument

set

An existing element or property has changed.

Callbacks will receive a function, done, and an object consisting of:

Property	Value
type	Enum 'set', denoting the event-type that was triggered
prevState	the previous state
nextState	the next state, i.e. the result of the add event that was captured

Fires on: Setting existing properties; mutating indexed accessors

del

An element or property has been deleted.

Callbacks will receive a function, done, and an object consisting of:

Property	Value
type	String "del", denoting the event-type that was triggered
prevState	the previous state
nextState	the next state, i.e. the result of the add event that was captured

Fires on: methods such as pop; delete called on a property

batched

A batched event has occurred. Batched events are those which carry several state changes as the result of a single action. For example, Array.prototype.unshift may prepend an element and shifts each element. Similarly, Array.prototype.push may be a batched event if provided more than a single argument.

Callbacks will receive a function, done, and an object consisting of:

Property	Value
type	String "batched", denoting the event-type that was triggered
prevState	the previous state
nextState	the next state, i.e. the result of the add event that was captured

Fires on: methods such as shift, unshift, push when called with multiple elements

Methods

Methods bound to all vivisected objects:

subscribe (eventName: ISubscriptionEvent, handler: ISubscriptionCallback, opts?: ISubscriptionOpts) => IVivisectorApi

Bind the callback handler to fire whenever an event of eventName has been triggered.

Options:

Property	Value
alwaysCommit?	a boolean indicating whether this action will always commit its state transitions. defaults to false

Throws when: provided an invalid event type or non-function handler

Example:

const logMsg = function (event, done) {
  // every time an item is added to the array, fire this callback
  console.log(`Added item such that ${event.prevState} becomes ${event.nextState}`);
  if (event.nextState.length) done(true);
});

const languages = vivisect(['C', 'Go']).subscribe('add', logMsg);

languages.push('JavaScript');
// "Added item such that ['C','Go'] becomes ['C','Go', 'JavaScript']"

unsubscribe (eventName: ISubscriptionEvent, handler: ISubscriptionCallback, opts?: ISubscriptionOpts) => IVivisectorApi

Remove an existing callback from the respective event-type to which it has been registered.

Options: n/a

Throws when: provided an invalid event type or non-function handler

Example:

const logMsg = function (event) {
  ...
});

const queens = vivisect(['RuPaul', 'Alaska'])
  .subscribe('add', logMsg, { alwaysCommit: true })
  .unsubscribe('add', logMsg);

queens.push('Bianca Del Rio');
// no log - handler was removed ^

State Commitment

As we've seen throughout the documentation, Vivisector events provide the opportunity to commit or revert state mutations. Every event callback is provided a done function with the following signature:

done (commit: boolean)

You'll have the opportunity to preview what the state transition would be by inspecting the nextState property. Then, you may programmatically commit the transition by passing true to the done function.

Passing false or not invoking done at all will revert any state changes and nextState will not take effect. The exception to this rule is the alwaysCommit option, which may be passed when registering the callback.

What's Next for Vivisector?

Here's a short list of upcoming features...

• cancellable state mutations
• deferred and 'auto-async' state mutations
• queued events
• custom event types (bind specific and user-defined prototype methods)
• optional batching

Contributions and feature requests are always welcome!