Inferno is an insanely fast, 9kb React-like library for building high-performance user interfaces on both the client and server.

To quote a member of the React core team at Facebook:

Inferno 1.0 is really well written. It's how I would've rewritten React. I'd recommend reading its source to learn.

Inferno aims to provide all the great benefits that React does, plus other great features for people already familiar with the React ecosystem, such as: lifecycle events on functional components, server side render streams, better real-world performance, lower memory consumption and faster parse/load times. Furthermore, Inferno allows people to switch their existing React projects to Inferno in a few lines of code using inferno-compat.

For those not familiar with React, Inferno is a JavaScript library for building user interfaces in a declarative manner. Rather than working with MVC/MVVM style patterns, Inferno uses a component-based approach where data flows in one direction, making coding predictable, re-usable and highly testable. Based on the concept of learn once, write anywhere, Inferno doesn't impose any restrictions on how you create components. You literally write JavaScript to state how you'd like your UI to look – Inferno does all the rest. Inferno also renders content on the server via inferno-server and NodeJS, so you can write awesome UIs that get rendered full-stack.

In terms of performance, Inferno is currently the fastest JavaScript UI library there is – both in benchmarks and actual real-world scenarios. It excels on the browser at initial page load, parse times, render times and update times. Inferno's server-side rendering is around 5x faster than React, around 3x faster than Angular 2 and around 1.5x faster than Preact and Vue.

But why?

Inferno started as an idea two years ago, to see if a UI library could really improve the experience, battery, memory usage and performance on mobile devices. At the time we really struggled to get good performance on any UI library/framework – it simply wasn't happening, we spent a huge amount of time writing lots of vanilla JavaScript code and it did the job – but it was a mess.

Since then, things haven't really improved much in the mobile space. Libraries have gotten smaller, but the time to parse a 2mb app can result in 5+ seconds time before the user can even see anything. Frameworks and libraries need to lose bloat, they need to care about performance. Developing on a MacBook Pro and seeing animations, routing, complex UIs instantly appear is not going to happen on an average mobile device (especially in emerging countries).

Inferno proves that it is possible to be fast on mobile. Parse-time, load-time, rendering complex UIs and all the normal things you'd expect to just work. How Inferno does that is based on many factors, but ultimately Inferno's code is much better understood by modern JavaScript engines and can be highly optimised to perform far better than other libraries/frameworks.

Summary

• Component driven + one-way data flow architecture
• One of the fastest front-end frameworks for rendering UI in the DOM
• React-like API, concepts and component lifecycle events
• Partial synthetic event system, providing delegation to certain events for better performance
• Inferno's linkEvent feature removes the need to use arrow functions or binding event callbacks
• Lightweight filesize of only 9kb
• Isomorphic rendering on both client and server with inferno-server
• Highly modular with very few opinions on how things should be done
• Unlike React and Preact, Inferno has lifecycle events on functional components
• Supports asynchronous component rendering using requestIdleCallback
• Unlike Preact and other React-like libraries, Inferno has controlled components for input/select/textarea elements

Benchmarks

• Virtual DOM Benchmark
• UI Bench
• dbmonster
• JS Web Frameworks Benchmark - Round 4

Code Example

Let's start with some code. As you can see, Inferno intentionally keeps the same, good, design ideas as React regarding components: one-way data flow and separation of concerns.

In these examples, JSX is used via the Inferno JSX Babel Plugin to provide a simple way to express Inferno virtual DOM. You do not need to use JSX, it's completely optional, you can use hyperscript or createElement (like React does).

import Inferno from 'inferno';

const message = "Hello world";

Inferno.render(
  <MyComponent message={ message } />,
  document.getElementById("app")
);

Furthermore, Inferno also uses ES6 components like React:

import Inferno from 'inferno';
import Component from 'inferno-component';

class MyComponent extends Component {
  constructor(props) {
    super(props);
    this.state = {
      counter: 0
    }
  }
  render() {
    return (
      <div>
        <h1>Header!</h1>
        <span>Counter is at: { this.state.counter }</span>
      </div>
    )
  }
}

Inferno.render(
  <MyComponent />,
  document.getElementById("app")
);

More Examples

• Simple Clock (@JSFiddle)

Getting Started

The best way to start to use Inferno is by using Create Inferno App. You can get setup and running within a few minutes.

Alternatively, you can get started with Inferno using the Inferno Boilerplate for a very simple setup. For a more advanced example demonstrating how Inferno might be used, we recommend trying out Inferno Starter Project by nightwolfz. For using inferno to build a mobile app Inferno Mobile Starter Project by Rudy-Zidan.

Core package:

npm install --save inferno

Addons:

# ES2015 class components
npm install --save inferno-component
# server-side rendering
npm install --save inferno-server
# routing
npm install --save inferno-router

Pre-bundled files for browser consumption can be found on our cdnjs:

https://cdnjs.cloudflare.com/ajax/libs/inferno/1.2.2/inferno.min.js

Or on unpkg.com:

https://unpkg.com/[email protected]/dist/inferno.min.js

Creating Virtual DOM

JSX:

npm install --save-dev babel-plugin-inferno

Hyperscript:

npm install --save inferno-hyperscript

createElement:

npm install --save inferno-create-element

Compatibility with existing React apps

npm install --save-dev inferno-compat

Note: Make sure you read more about inferno-compat before using it.

Third-party state libraries

Inferno now has bindings available for some of the major state management libraries out there:

• Redux via inferno-redux
• MobX via inferno-mobx
• Cerebral via cerebral-view-inferno

JSX

Inferno has its own JSX Babel plugin.

Differences from React

• Inferno is much smaller in size, 9kb vs 45kb gzip. This means Inferno is faster to transfer over the network but more importantly, is much faster to parse – this makes a big impact on mobile.
• Inferno is considerably faster than React. This doesn't apply to only benchmarks, but real-world applications that companies have converted to Inferno from React. Ranging from 40% - 110% performance improvement with Inferno 1.0. No other React-like library gets close to this performance gain over React.
• Inferno doesn't have a fully synthetic event system like React does. Inferno has a partially synthetic event system, instead opting to only delegate certain events (such as onClick).
• Inferno doesn't support React Native. Inferno was only designed for the browser/server with the DOM in mind.
• Inferno doesn't support string refs – although this can be enabled using inferno-compat. We don't recommend using them, they are the source of many memory leaks and performance issues in real-world apps. Stick with function callback refs instead.
• Inferno includes render on the main core package, rather than have an InfernoDOM package like React does. We used to do it that way, but we found people simply didn't like it given we don't support native. Furthermore, by not splitting them, we improved performance and bundle sizes.
• Inferno provides lifecycle events on functional components. This is a major win for people who prefer lightweight components rather than bloated ES2015 classes.
• Inferno is able to use the React Dev Tools extensions for Chrome/Firefox/etc to provide the same level of debugging experience to user of Inferno via inferno-devtools.

Differences from Preact

• Inferno is larger in size, 9kb vs 3kb gzip. This means that Preact should parse faster than Inferno – if only slightly.
• Inferno has a partial synthetic event system, resulting in better performance via delegation of certain events.
• Inferno is much faster than Preact in rendering, updating and removing elements from the DOM. Inferno diffs against virtual DOM, rather than the real DOM (except for when loading from server-side rendered content) which means it can make drastic improvements. Unfortunately, diffing against the real DOM has a 30-40% overhead cost in operations.
• Inferno fully supports controlled components for input/select/textarea elements. This prevents lots of edgecases where the virtual DOM is not the source of truth (it should always be). Preact pushes the source of truth to the DOM itself.
• Inferno provides lifecycle events on functional components. This is a major win for people who prefer lightweight components rather than bloated ES2015 classes.

Event System

Like React, Inferno also uses a light-weight synthetic event system in certain places (although both event systems differ massively). Inferno's event system provides highly efficient delegation and an event helper called linkEvent.

One major difference between Inferno and React is that Inferno does not rename events or change how they work by default. Inferno only specifies that events should be camel cased, rather than lower case. Lower case events will bypass Inferno's event system in favour of using the native event system supplied by the browser. For example, when detecting changes on an <input> element, in React you'd use onChange, with Inferno you'd use onInput instead (the native DOM event is oninput).

This feature is a very recent addition to Inferno, so there are only a handful of events that use Inferno's event system:

• onClick
• onDblClick
• onMouseMove
• onMouseDown
• onMouseUp
• onSubmit
• onKeyPress
• onKeyDown
• onKeyUp
• onInput
• onChange

More events are expected to be supported in future versions.

Controlled Components

In HTML, form elements such as <input>, <textarea>, and <select> typically maintain their own state and update it based on user input. In Inferno, mutable state is typically kept in the state property of components, and only updated with setState().

We can combine the two by making the Inferno state be the "single source of truth". Then the Inferno component that renders a form also controls what happens in that form on subsequent user input. An input form element whose value is controlled by Inferno in this way is called a "controlled component".

Inferno Top-Level API

render (package: inferno)

import Inferno from 'inferno';

Inferno.render(<div />, document.getElementById("app"));

Render a virtual node into the DOM in the supplied container given the supplied virtual DOM. If the virtual node was previously rendered into the container, this will perform an update on it and only mutate the DOM as necessary, to reflect the latest Inferno virtual node.

Warning: If the container element is not empty before rendering, the content of the container will be overwritten on the initial render.

createRenderer (package: inferno)

createRenderer allows for functional composition when rendering content to the DOM. Example:

import Inferno from 'inferno';
import { scan, map } from 'most';

...
const model$ = scan(update, 0, actions$);
const vNodes$ = map(view(actions$), model$);
const renderer = Inferno.createRenderer();
const runApp = () => scan(renderer, container, vNodes$).drain();

runApp();

createElement (package: inferno-create-element)

Creates an Inferno VNode using a similar API to that found with React's createElement()

import Component from 'inferno-component';
import createElement from 'inferno-create-element';

class BasicComponent extends Component {
    render() {
        return createElement('div', {
               className: 'basic'
           },
           createElement('span', {
               className: this.props.name
           }, 'The title is ', this.props.title)
       )
    }
}

Inferno.render(
  createElement(BasicComponent, { title: 'abc' }),
  document.getElementById("app")
);

Component (package: inferno-component)

Class component:

import Component from 'inferno-component';

class MyComponent extends Component {
  render() {
    ...
  }
}

This is the base class for Inferno Components when they're defined using ES6 classes.

Functional component:

import Inferno from 'inferno';

const MyComponent = ({ name, age }) => (
  <span>My name is: { name } and my age is: {age}</span>
);

Functional components are first-class functions where their first argument is the props passed through from their parent.

createVNode (package: inferno)

Inferno.createVNode(
  flags,
  type,
  [props],
  [...children],
  [events],
  [key],
  [ref],
  [isNormalized]
)

Create a new Inferno VNode using createVNode(). A VNode is a virtual DOM object that is used to describe a single element of the UI. Typically createElement() (package: inferno-create-element), h() (package: inferno-hyperscript) or JSX are used to create VNodes for Inferno, but under the hood they all use createVNode(). Below is an example of using of createVNode usage:

import Inferno from 'inferno';

const vNode = Inferno.createVNode(2, 'div', { className: 'example' }, 'Hello world!');

Inferno.render(vNode, container);

The first argument for createVNode() is a value from VNodeFlags, this is a numerical value that tells Inferno what the VNode describes on the page.

cloneVNode (package: inferno)

Inferno.cloneVNode(
  vNode,
  [props],
  [...children]
)

Clone and return a new Inferno VNode using a VNode as the starting point. The resulting VNode will have the original VNode's props with the new props merged in shallowly. New children will replace existing children. key and ref from the original VNode will be preserved.

cloneVNode() is almost equivalent to:

<VNode.type {...VNode.props} {...props}>{children}</VNode.type>

An example of using cloneVNode:

import Inferno from 'inferno';

const vNode = Inferno.createVNode(2, 'div', { className: 'example' }, 'Hello world!');
const newVNode = Inferno.cloneVNode(vNode, { id: 'new' }); // we are adding an id prop to the VNode

Inferno.render(newVNode, container);

If you're using JSX:

import Inferno from 'inferno';

const vNode = <div className="example">Hello world</div>;
const newVNode = Inferno.cloneVNode(vNode, { id: 'new' }); // we are adding an id prop to the VNode

Inferno.render(newVNode, container);

findDOMNode (package: inferno)

Once enabled via Inferno.options.findDOMNodeEnabled = true; at the start of an application, findDOMNode() is enabled.

Note: we recommend using a ref callback on a component to find its instance, rather than using findDOMNode(). findDOMNode() cannot be used on functional components and it introduces a significant performance impact.

If a component has been mounted into the DOM, this returns the corresponding native browser DOM element. This method is useful for reading values out of the DOM, such as form field values and performing DOM measurements. In most cases, you can attach a ref to the DOM node and avoid using findDOMNode() at all. When render returns null or false, findDOMNode() returns null.

linkEvent (package: inferno)

linkEvent() is a helper function that allows attachment of props/state/context or other data to events without needing to bind() them or use arrow functions/closures. This is extremely useful when dealing with events in functional components. Below is an example:

import Inferno, { linkEvent } from 'inferno';

function handleClick(props, event) {
	props.validateValue(event.target.value);
}

function MyComponent(props) {
	return <div><input type="text" onClick={ linkEvent(props, handleClick) } /><div>;
}

This is an example of using it with ES2015 classes:

import Inferno, { linkEvent } from 'inferno';
import Component from 'inferno-component';

function handleClick(instance, event) {
	instance.setState({ data: event.target.value });
}

class MyComponent extends Component {
	render () {
		return <div><input type="text" onClick={ linkEvent(this, handleClick) } /><div>;
	}
}

linkEvent() offers better performance than binding an event in a class constructor and using arrow functions, so use it where possible.

renderToString (package: inferno-server)

import Inferno from 'inferno';
import InfernoServer from 'inferno-server';

InfernoServer.renderToString(<div />);

Render a virtual node into an HTML string, given the supplied virtual DOM.

options (package: inferno)

You can set default options for Inferno using Inferno.options. Below are the following options:

- findDOMNodeEnabled (default: false)

This enables findDOMNode(). We strongly recommend against using this API as it introduces a significant impact to performance. In the future this API command will be removed, along with findDOMNode();

- recyclingEnabled (default: true)

This enables DOM node recycling within Inferno, so that DOM nodes are re-used upon disposal. It can have significant performance benefits, but may also cause side-effects with custom elements.

Functional component lifecycle events

| Name | Triggered when | Arguments to callback | | ----------- | -------------- | ----------------------- | | onComponentWillMount | a functional component is about to mount | | | onComponentDidMount | a functional component has mounted successfully | domNode | | onComponentShouldUpdate | a functional component has been triggered to updated | lastProps, nextProps | | onComponentWillUpdate | a functional component is about to perform an update | lastProps, nextProps | | onComponentDidUpdate | a functional component has performed an updated | lastProps, nextProps | | onComponentWillUnmount | a functional component is about to be unmounted | domNode |

Using functional lifecycle events

Functional lifecycle events must be explicitly assigned via props onto a functional component like shown below:

function mounted(domNode) {
    // [domNode] will be available for DOM nodes and components (if the component has mounted to the DOM)
}

function FunctionalComponent({ props }) {
	return <div>Hello world</div>;
}

Inferno.render(
  <FunctionalComponent onComponentDidMount={ mounted } />,
  document.getElementById("app")
);

Please note: class components (ES2015 classes) from inferno-component do not support the same lifecycle events (they have their own lifecycle events that work as methods on the class itself).

Development vs Production modes

By default, Inferno will run in development mode. Development mode provides extra checks and better error messages at the cost of slower performance and larger code to parse. When using Inferno in a production environment, it is highly recommended that you turn off development mode.

Running Inferno on Node JS

Ensure the environment variable process.env.NODE_ENV is set to production.

Building Inferno for use in a browser

When running Inferno on the browser using Webpack or Rollup, a replacement will need to occur during your build.

Webpack

Use the following configuration in your Webpack build:

  ...
	plugins: [
    new webpack.DefinePlugin({
      'process.env': {
        'NODE_ENV': JSON.stringify('production')
      }
    })
  ]

Rollup

Use the following configuration in your Rollup build:

const replace = require('rollup-plugin-replace');

  ...
	plugins: [
		replace({
			'process.env.NODE_ENV': JSON.stringify('production'),
		})
  ]

Browser Support

Inferno supports Edge, Chrome, Firefox and Safari 8+. In order to support IE8-11, Inferno may require polyfills for the following JavaScript features:

• Promise object
• Map object
• WeakMap object
• Object.keys

Potential solutions include using the es5-shim for ES5 features and es6-shim from ES2015 features.

As a quick drop-in solution, you may also use the Polyfill.io service to pull in the required polyfills for the user's browser automatically by including the following line in your page:

<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=Promise,Map,WeakMap,Object.keys"></script>

Custom namespaces

Inferno wants to always deliver great performance. In order to do so, it has to make intelligent assumptions about the state of the DOM and the elements available to mutate. Custom namespaces conflict with this idea and change the schema of how different elements and attributes might work, so Inferno makes no attempt to support namespaces. Instead, SVG namespaces are automatically applied to elements and attributes based on their tag name.

Community

There is an Inferno Slack. You can join via inferno-slack.herokuapp.com.