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

The main objective of the Inferno project is to provide the fastest possible runtime performance for web applications. Inferno excels at rendering real time data views or large DOM trees.

The performance is achieved through multiple optimizations, for example:

• Inferno's own JSX plugin creates monomorphic createVNode calls, instead of createElement
• Inferno's diff process uses bitwise flags to memoize the shape of objects
• Child nodes are normalized only when needed
• Special JSX flags can be used during compile time to optimize runtime performance at application level
• Many micro optimizations

• Component driven + one-way data flow architecture
• React-like API, concepts and component lifecycle events
• Partial synthetic event system, normalizing events for better cross browser support
• Inferno's linkEvent feature removes the need to use arrow functions or binding event callbacks
• Isomorphic rendering on both client and server with inferno-server
• Unlike React and Preact, Inferno has lifecycle events on functional components
• Unlike Preact and other React-like libraries, Inferno has controlled components for input/select/textarea elements
• Components can be rendered outside their current html hierarchy using createPortal - API
• Support for older browsers without any polyfills
• defaultHooks for Functional components, this way re-defining lifecycle events per usage can be avoided

Since version 4 we have started running our test suite without any polyfills. Inferno is now part of Saucelabs open source program and we use their service for executing the tests.

InfernoJS natively supports the browsers listed below.

List of breaking changes can be found from here

• UI Bench
• dbmonster
• JS Web Frameworks Benchmark - Round 7
• Isomorphic-UI-Benchmark
• 1k Components

Let's start with some code. As you can see, Inferno intentionally keeps the same 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). Keep in mind that compile time optimizations are available only for JSX.

import { render } from 'inferno';

const message = "Hello world";

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

Furthermore, Inferno also uses ES6 components like React:

import { render, Component } from 'inferno';

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>
    );
  }
}

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

Because performance is an important aspect of this library, we want to show you how to optimize your application even further. In the example below we optimize diffing process by using JSX $HasVNodeChildren to predefine children shape compile time. Then we create text vNode using createTextVNode. All child flags are documented here.

import { createTextVNode, render, Component } from 'inferno';

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

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

To tear down inferno application you need to render null on root element. Rendering null will trigger unmount lifecycle hooks for whole vDOM tree and remove global event listeners. It is important to unmount unused vNode trees to free browser memory.

import { createTextVNode, render, Component } from 'inferno';

const rootElement = document.getElementById("app");

// Start the application
render(
  <ExampleComponent/>,
  rootElement
);

// Tear down
render(
  null,
  rootElement
);

If you have built something using Inferno you can add them here:

• Simple Clock (@JSFiddle)

The best way to get started with Inferno is by using Create Inferno App.

Alternatively, you can try any of the following:

• 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, try Inferno Mobile Starter Project by Rudy-Zidan.
• for TypeScript support and bundling with Browserify: https://github.com/smcatala/inferno-typescript-browserify-example
• for an example of how to use Inferno in codesandbox: https://codesandbox.io/s/znmyj24w4p

Core package:

npm install --save inferno

Addons:

# 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:

Or on jsDelivr:

https://cdn.jsdelivr.net/npm/inferno@latest/dist/inferno.min.js

Or on unpkg.com:

https://unpkg.com/inferno@latest/dist/inferno.min.js

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

npm install --save inferno-hyperscript

npm install --save inferno-create-element

npm install --save-dev inferno-compat

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

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

Inferno has its own JSX Babel plugin.

• Inferno is much smaller in size, ~8kb vs 45kb gzip. This means Inferno is faster to transfer over the network but more importantly, it is much faster to parse – this makes a big impact on mobile.
• Inferno is considerably faster than React. This doesn't apply to benchmarks only, but to real-world applications that companies have converted to Inferno from React as well. 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 since 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 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 the Inferno user via inferno-devtools.

• Inferno is larger in size, ~8kb 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 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 ES2015 classes.

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).

Available synthetic events are:

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

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 { 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 { linkEvent, Component } from 'inferno';

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.

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".

import { render } from '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 creates an alternative render function with a signature matching that of the first argument passed to a reduce/scan function. This allows for easier integration with reactive programming libraries, like RxJS and Most.

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

const renderer = createRenderer();


// NOTE: vNodes$ represents a stream of virtual DOM node updates
scan(renderer, document.getElementById("app"), vNodes$);

See inferno-most-fp-demo for an example of how to build an app architecture around this.

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

import { Component, render } from 'inferno';
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)
    )
  }
}

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

Class component:

import { Component } from 'inferno';

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

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

Functional component:

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

Another way of using defaultHooks.

export function Static() {
    return <div>1</div>;
}

Static.defaultHooks = {
    onComponentShouldUpdate() {
        return false;
    }
};

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

import { createVNode } from 'inferno';

createVNode(
  flags,
  type,
  [className],
  [...children],
  [childFlags],
  [props],
  [key],
  [ref]
)

createVNode is used to create html element's virtual node object. 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 createVNode usage:

import { VNodeFlags, ChildFlags } from 'inferno-vnode-flags';
import { createVNode, createTextVNode, render } from 'inferno';

const vNode = createVNode(VNodeFlags.HtmlElement, 'div', 'example', createTextVNode('Hello world!'), ChildFlags.HasVNodeChildren);

// <div class="example">Hello world!</div>

render(vNode, container);

createVNode arguments explained:

flags: (number) is a value from VNodeFlags, this is a numerical value that tells Inferno what the VNode describes on the page.

type: (string) is tagName for element for example 'div'

className: (string) is the class attribute ( it is separated from props because it is the most commonly used property )

children: (vNode[]|vNode) is one or array of vNodes to be added as children for this vNode

childFlags: (number) is a value from ChildFlags, this tells inferno shape of the children so normalization process can be skipped.

props: (Object) is object containing all other properties. fe: {onClick: method, 'data-attribute': 'Hello Community!}

key: (string|number) unique key within this vNodes siblings to identify it during keyed algorithm.

ref: (function) callback which is called when DOM node is added/removed from DOM.

import { createComponentVNode } from 'inferno';

createComponentVNode(
  flags,
  type,
  [props],
  [key],
  [ref]
)

createComponentVNode is used for creating vNode for Class/Functional Component.

Example:

import { VNodeFlags, ChildFlags } from 'inferno-vnode-flags';
import { createVNode, createTextVNode, createComponentVNode, render } from 'inferno';

function MyComponent(props, context) {
  return createVNode(VNodeFlags.HtmlElement, 'div', 'example', createTextVNode(props.greeting), ChildFlags.HasVNodeChildren);
}

const vNode = createComponentVNode(VNodeFlags.ComponentFunction, MyComponent, {
  greeting: 'Hello Community!'
}, null, {
  onComponentDidMount() {
    console.log("example of did mount hook!")
  }
})

// <div class="example">Hello Community!</div>

render(vNode, container);

createComponentVNode arguments explained:

flags: (number) is a value from VNodeFlags, this is a numerical value that tells Inferno what the VNode describes on the page.

type: (Function/Class) is the class or function prototype for Component

props: (Object) properties passed to Component, can be anything

key: (string|number) unique key within this vNodes siblings to identify it during keyed algorithm.

ref: (Function|Object) this property is object for Functional Components defining all its lifecycle methods. For class Components this is function callback for ref.

createTextVNode is used for creating vNode for text nodes.

createTextVNode arguments explained: text: (string) is a value for text node to be created. key: (string|number) unique key within this vNodes siblings to identify it during keyed algorithm.

import { createTextVNode } from 'inferno';

createTextVNode(
  text,
  key
)

This package has same API as React.cloneElement

import {cloneVNode} from 'inferno-clone-vnode';

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 { cloneVNode, createVNode, render } from 'inferno';
import { VNodeFlags } from 'inferno-vnode-flags';

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

render(newVNode, container);

If you're using JSX:

import { render, cloneVNode } from 'inferno';

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

render(newVNode, container);

HTML:

<div id="root"></div>
<div id="outside"></div>

Javascript:

const { render, Component, version, createPortal } from 'inferno';

function Outsider(props) {
	return <div>{`Hello ${props.name}!`}</div>;
}

const outsideDiv = document.getElementById('outside');
const rootDiv = document.getElementById('root');

function App() {
	return (
  	    <div>
    	    Main view
            ...
            {createPortal(<Outsider name="Inferno" />, outsideDiv)}
        </div>
    );
}


// render an instance of Clock into <body>:
render(<App />, rootDiv);

Results into:

<div id="root">
    <div>Main view ...</div>
</div>
<div id="outside">
    <div>Hello Inferno!</div>
</div>

Cool huh? Updates (props/context) will flow into "Outsider" component from the App component the same way as any other Component. For inspiration on how to use it click here!

import { hydrate } from 'inferno';

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

Same as render(), but is used to hydrate a container whose HTML contents were rendered by inferno-server. Inferno will attempt to attach event listeners to the existing markup.

This feature has been moved from inferno to inferno-compat in v4 forward. No options are needed anymore.

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.

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.

VNodeFlags:

• VNodeFlags.HtmlElement
• VNodeFlags.ComponentUnknown
• VNodeFlags.ComponentClass
• VNodeFlags.ComponentFunction
• VNodeFlags.Text
• VNodeFlags.SvgElement
• VNodeFlags.InputElement
• VNodeFlags.TextareaElement
• VNodeFlags.SelectElement
• VNodeFlags.Void
• VNodeFlags.Portal
• VNodeFlags.ReCreate (JSX $ReCreate) always re-creates the vNode

VNodeFlags Masks:

• VNodeFlags.FormElement - Is from element
• VNodeFlags.Element - Is vNode element
• VNodeFlags.Component - Is vNode Component
• VNodeFlags.VNodeShape - mask for defining type

ChildFlags

• ChildFlags.UnknownChildren needs Normalization
• ChildFlags.HasInvalidChildren is invalid (null, undefined, false, true)
• ChildFlags.HasVNodeChildren (JSX $HasVNodeChildren) is single vNode (Element/Component)
• ChildFlags.HasNonKeyedChildren (JSX $HasNonKeyedChildren) is Array of vNodes non keyed (no nesting, no holes)
• ChildFlags.HasKeyedChildren (JSX $HasKeyedChildren) is Array of vNodes keyed (no nesting, no holes)

ChildFlags Masks

• ChildFlags.MultipleChildren Is Array

import { renderToString } from 'inferno-server';

const string = renderToString(<div />);

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

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

import { render } from 'inferno';

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>;
}

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

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

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.

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

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

Use the following configuration in your Webpack build for production build:

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

When you are building for development, you may want to use inferno.dev.esm.js ("dev:module": "dist/index.dev.esm.js",) file. That build version has extra level of validation for development purposes. You can use it by adding following code to your webpack config.

    ...
	resolve: {
    /* When doing development workflow we want to make sure webpack picks up development build of inferno */
		alias: {
			inferno: __dirname + "/node_modules/inferno/dist/index.dev.esm.js"
		}
	}

Use the following configuration in your Rollup build:

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

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

When you are building for development, you may want to use inferno.dev.esm.js ("dev:module": "dist/index.dev.esm.js",) file. That build version has extra level of validation for development purposes. You can use it by adding following code to your rollup config.

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

    ...
  plugins: [
    alias({
      'inferno': __dirname + '/node_modules/inferno/dist/index.dev.esm.js'
    }),
  ]

Inferno always wants to 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.

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

This project exists thanks to all the people who contribute. [Contribute].

Thank you to all our backers! 🙏 [Become a backer]

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