Building User Interfaces: React, Vue, Preact, and Inferno Compared

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

Description

The main objective of the InfernoJS 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 compilers creates monomorphic createVNode calls, instead of createElement calls. Optimizing runtime performance of the application.
  • SWC plugin inferno is a plugin for SWC. It can compile TSX and JSX
  • Babel plugin inferno is a plugin for BabelJs. It can compile JSX.
  • TS plugin inferno is a plugin for TSC. It can compile TSX.
• 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

Features

• 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
• Inferno supports setting styles using string <div style="background-color: red"></div> or using object literal syntax <div style={{"background-color": "red"}}></div>. For camelCase syntax support see inferno-compat.
• Fragments (v6)
• createRef and forwardRef APIs (v6)
• componentDidAppear, componentWillDisappear and componentWillMove (v8) - class and function component callbacks to ease animation work, see inferno-animation package

Runtime requirements

Inferno v9 requires following features to be present in the executing runtime:

• Promise
• String.prototype.includes()
• String.prototype.startsWith()
• Array.prototype.includes()
• Object.spread()

Browser support

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 is actively tested with browsers listed below, however it may run well on older browsers as well. This is due to limited support of browser versions in recent testing frameworks. https://github.com/jasmine/jasmine/blob/main/release_notes/5.0.0.md

Migration guides

• Inferno v4
• Inferno v6

Benchmarks

Live examples at https://infernojs.github.io/inferno

• UI Bench
• dbmonster
• JS Web Frameworks Benchmark (current)
• Isomorphic-UI-Benchmark
• 1k Components

Code Example

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 and $HasTextChildren to predefine children shape compile time. In the MyComponent render method there is a div that contains JSX expression node as its content. Due to dynamic nature of Javascript that variable node could be anything and Inferno needs to go through the normalization process to make sure there are no nested arrays or other invalid data. Inferno offers a feature called ChildFlags for application developers to pre-define the shape of vNode's child node. In this example case it is using $HasVNodeChildren to tell the JSX compiler, that this vNode contains only single element or component vNode. Now inferno will not go into the normalization process runtime, but trusts the developer decision about the shape of the object and correctness of data. If this contract is not kept and node variable contains invalid value for the pre-defined shape (fe. null), then application would crash runtime. There is also span-element in the same render method, which content is set dynamically through _getText() method. There $HasTextChildren child-flag fits nicely, because the content of that given "span" is never anything else than text. All the available child flags are documented here.

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

class MyComponent extends Component {
  constructor(props) {
    super(props);
    this.state = {
      counter: 0,
    };
  }

  _getText() {
    return 'Hello!';
  }

  render() {
    const node =
      this.state.counter > 0 ? (
        <div>0</div>
      ) : (
        <span $HasTextChildren>{this._getText()}</span>
      );

    return (
      <div>
        <h1>Header!</h1>
        <div $HasVNodeChildren>{node}</div>
      </div>
    );
  }
}

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

Tear down

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);

More Examples

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

• Simple Clock (@JSFiddle)
• Simple JS Counter (@github/scorsi): SSR Inferno (view) + Cerebral (state manager) + FuseBox (build system/bundler)
• Online interface to TMDb movie database (@codesandbox.io): Inferno + Inferno hyperscript (view) + Superagent (network requests) + Web component (custom elements v1) + state-transducer (state machine library)
• Lemmy - a self-hostable reddit alternative (front end in Inferno)

Getting Started

The easiest 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, check out ts-plugin-inferno, or inferno-typescript-example.
• for an example of how to use Inferno in codesandbox: https://codesandbox.io/s/znmyj24w4p
• for using parcel and typescript

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

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/inferno

JSX

Inferno has its own JSX Babel plugin.

Differences from 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 legacy string refs, use createRef or callback ref API
• Inferno provides lifecycle events on functional components. This is a major win for people who prefer lightweight components rather than ES2015 classes.

Differences from Preact

• 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.

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).

Available synthetic events are:

• onClick
• onDblClick
• onFocusIn
• onFocusOut
• onKeyDown
• onKeyPress
• onKeyUp
• onMouseDown
• onMouseMove
• onMouseUp
• onTouchEnd
• onTouchMove
• onTouchStart

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 { 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.

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 { 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 (package: inferno)

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.

createElement (package: inferno-create-element)

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'),
);

Component (package: inferno)

Class component:

import { Component } from 'inferno';

class MyComponent extends Component {
  render() {
    return <div>My Component</div>;
  }
}

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;
  },
};

Default props

export function MyFunctionalComponent({ value }) {
  return <div>{value}</div>;
}

MyFunctionalComponent.defaultProps = {
  value: 10,
};

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

createVNode (package: inferno)

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.

createComponentVNode (package: 'inferno')

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 (package: 'inferno')

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);

cloneVNode (package: inferno-clone-vnode)

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

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);

createPortal (package: 'inferno')

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!

createRef (package: inferno)

createRef API provides shorter syntax than callback ref when timing of element is not needed.

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

class Foobar extends Component {
  constructor(props) {
    super(props);

    // Store reference somewhere
    this.element = createRef(); // Returns object {current: null}
  }

  render() {
    return (
      <div>
        <span id="span" ref={this.element}>
          Ok
        </span>
      </div>
    );
  }
}

render(<Foobar />, container);

createFragment (package: inferno)

createFragment is the native way to createFragment vNode. createFragment(children: any, childFlags: ChildFlags, key?: string | number | null)

createFragment arguments explained:

children: (Array) Content of fragment vNode, typically array of VNodes

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

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

Alternative ways to create fragment vNode are:

• Using JSX <> ... </>, <Fragment> .... </Fragment> or <Inferno.Fragment> ... </Inferno.Fragment>
• Using createElement API createElement(Inferno.Fragment, {key: 'test'}, ...children)
• Using hyperscript API h(Inferno.Fragment, {key: 'test'}, children)

In the below example both fragments are identical except they have different key

import { Fragment, render, createFragment } from 'inferno';
import { ChildFlags } from 'inferno-vnode-flags';

function Foobar() {
  return (
    <div $HasKeyedChildren>
      {createFragment(
        [<div>Ok</div>, <span>1</span>],
        ChildFlags.HasNonKeyedChildren,
        'key1',
      )}
      <Fragment key="key2">
        <div>Ok</div>
        <span>1</span>
      </Fragment>
    </div>
  );
}

render(<Foobar />, container);

forwardRef (package: inferno)

forwardRef is a new mechanism to "forward" ref inside a functional Component. It can be useful if you have simple functional Components and you want to create reference to a specific element inside it.

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

const FancyButton = forwardRef((props, ref) => (
  <button ref={ref} className="FancyButton">
    {props.children}
  </button>
));

class Hello extends Component {
  render() {
    return (
      <FancyButton
        ref={(btn) => {
          if (btn) {
            // btn variable is the button rendered from FancyButton
          }
        }}
      >
        Click me!
      </FancyButton>
    );
  }
}

render(<Hello />, container);

hydrate (package: inferno-hydrate)

import { hydrate } from 'inferno-hydrate';

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.

findDOMNode (package: inferno-extras)

This feature has been moved from inferno to inferno-compat in v6. 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. If Component has rendered fragment it returns the first element.

Inferno Flags (package: inferno-vnode-flags)

VNodeFlags:

• VNodeFlags.HtmlElement
• VNodeFlags.ComponentUnknown
• VNodeFlags.ComponentClass
• VNodeFlags.ComponentFunction
• VNodeFlags.Text
• VNodeFlags.SvgElement
• VNodeFlags.InputElement
• VNodeFlags.TextareaElement
• VNodeFlags.SelectElement
• VNodeFlags.Portal
• VNodeFlags.ReCreate (JSX $ReCreate) always re-creates the vNode
• VNodeFlags.ContentEditable
• VNodeFlags.Fragment
• VNodeFlags.InUse
• VnodeFlags.ForwardRef
• VNodeFlags.Normalized

VNodeFlags Masks:

• VNodeFlags.ForwardRefComponent Functional component wrapped in forward ref
• VNodeFlags.FormElement - Is form element
• VNodeFlags.Element - Is vNode element
• VNodeFlags.Component - Is vNode Component
• VNodeFlags.DOMRef - Bit set when vNode holds DOM reference
• VNodeFlags.InUseOrNormalized - VNode is used somewhere else or came from normalization process
• VNodeFlags.ClearInUseNormalized - Opposite mask of InUse or Normalized

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.HasTextChildren (JSX $HasTextChildren) vNode contains only text

ChildFlags Masks

• ChildFlags.MultipleChildren Is Array

renderToString (package: inferno-server)

import { renderToString } from 'inferno-server';

const string = renderToString(<div />);

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

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 update	lastProps, nextProps
onComponentWillUpdate	a functional component is about to perform an update	lastProps, nextProps
onComponentDidUpdate	a functional component has performed an update	lastProps, nextProps
onComponentWillUnmount	a functional component is about to be unmounted	domNode
onComponentDidAppear	a functional component has mounted and is ready for animations	domNode, props
onComponentWillDisappear	a functional component is unmounted before DOM node is removed	domNode, props, callback

onComponentWillDisappear has special type of argument "callback" which needs to be called when component is ready to be removed from the DOM. fe. after animations are finished.

Class component lifecycle events

All these Component lifecycle methods ( including render and setState - callback) are called with Component instance context. You don't need to "bind" these methods.

Name	Triggered when	Arguments to callback
componentDidMount	component has been mounted successfully
componentWillMount	component is about to mount
componentWillReceiveProps	before render when component updates	nextProps, context
shouldComponentUpdate	component has been triggered to update	nextProps, nextState
componentWillUpdate	component is about to perform an update	nextProps, nextState, context
componentDidUpdate	component has performed an update	lastProps, lastState, snapshot
componentWillUnmount	component is about to be unmounted
getChildContext	before render method, return value object is combined to sub tree context
getSnapshotBeforeUpdate	before component updates, return value is sent to componentDidUpdate as 3rd parameter	lastProps, lastState
static getDerivedStateFromProps	before render method	nextProps, state
componentDidAppear	component has mounted and is ready for animations	domNode
componentWillDisappear	component is unmounted before DOM node is removed	domNode, callback

componentWillDisappear has special type of argument "callback" which needs to be called when component is ready to be removed from the DOM. fe. after animations are finished.

Using functional lifecycle events

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).

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.

Application bundling

When building your application bundle, ensure process.env.NODE_ENV is replaced with string"development" or "production" based on the workflow. It is recommended to use ts-plugin-inferno for typescript TSX compilation and babel-plugin-infeno for javascript JSX compilation.

When building for development, you may want to use inferno.dev.mjs for v9 or newer and inferno.dev.esm.js for older than v9. That bundle file contains ES6 exports for better tree-shaking support, improved error messages and added validation to help fixing possible issues during development. The file is found from package.json - dev:module entry point and the files are physically located in node_modules/inferno/dist/ folder. Remember that it is not recommended to use that file in production due to slower performance. For production usage use node_modules/inferno/dist/inferno.mjs -file for v9 or newer and node_modules/inferno/dist/inferno.esm.js -file for older than v9.

Example of Webpack configuration:

const path = require('path');
const infernoTsx = require('ts-plugin-inferno').default;

... webpack config ...

    module: {
        rules: [
            {
                test: /\.js$/, // Add "jsx" if your application uses `jsx` file extensions
                exclude: /node_modules/,
                use: [{
                    loader: 'babel-loader',
                    options: {
                        plugins: [
                            // Compile javascript JSX syntax using inferno's own plugin
                            ['babel-plugin-inferno', {imports: true}]
                        ]
                    }
                }]
            },
            {
                test: /\.ts+(|x)$/, // Compile ts and tsx extensions
                exclude: /node_modules/,
                use: [{
                    loader: 'ts-loader',
                    options: {
                        getCustomTransformers: () => ({
                            // inferno custom TSX plugin
                            after: [infernoTsx()]
                        }),
                        compilerOptions: {
                            /* typescript compiler options */
                        }
                    }
                }]
            }
        ]
    },
    resolve: {
        extensions: ['.js', '.ts', '.tsx'],
        alias: {
            // This maps import "inferno" to es6 module entry based on workflow
            inferno: path.resolve(__dirname, 'node_modules/inferno/dist', isProduction ? 'index.dev.mjs' : 'index.mjs')
        }
    },
    plugins: [
        new webpack.DefinePlugin({
            'process.env': {
                'NODE_ENV':  JSON.stringify(isProduction ? 'production' : 'development')
            }
        })
    ]

Example of Rollup configuration:

const path = require('path');
const alias = require('@rollup/plugin-alias');
const {babel} = require('@rollup/plugin-babel');
const replace = require('@rollup/plugin-replace');
const typescript = require('rollup-plugin-typescript2');
const transformInferno = require('ts-plugin-inferno').default;

... Rollup config ...
{
    input: /* entry file */,
    plugins: [
            alias({
                resolve: ['.js'],
                entries: [
                    // This maps import "inferno" to es6 module entry based on workflow
                    {find: 'inferno', replacement: path.resolve(__dirname, 'node_modules/inferno/dist', isProduction ? 'index.dev.mjs' : 'index.mjs')}
                ]
            }),
            typescript({
                include: ['*.ts+(|x)', '**/*.ts+(|x)'],
                transformers: [
                    () => ({
                        after: [transformInferno()]
                    })
                ],
                tsconfig: 'tsconfig.json',
                tsconfigOverride: {
                    /* typescript compiler options */
                }
            }),
            babel({
                babelrc: false,
                sourceMaps: isDeploy,
                plugins: [
                    // Compile javascript JSX syntax using inferno's own plugin
                    ['babel-plugin-inferno', {imports: true}]
                ],
                babelHelpers: 'bundled'
            })
    ]
}

Custom namespaces

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.

Development

If you want to contribute code, fork this project and submit a PR from your fork. To run browser tests you need to build the repos. A complete rebuild of the repos can take >5 mins.

$ git clone git@github.com:infernojs/inferno.git
$ cd inferno && npm i
$ npm run test:node
$ npm run build
$ npm run test:browser

If you only want to run the browser tests when coding, use the following to reduce turnaround by 50-80%:

$ npm run quick-test:browser # Compiles all packages and runs browser tests
$ npm run quick-test:browser-inferno # Only compiles the inferno package and runs browser tests
$ npm run quick-test:browser-debug # Compiles all packages and runs browser tests with "debug"

Community

There is an InfernoJS Discord. You can join via https://discord.gg/SUKuhgaBpF.

Contributors

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

Backers

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

Sponsors

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