Simple way to build a custom React renderer

$ npm install reconciled

Here's a minimal version of react-dom implemented with reconciled without support for updates or events:

import reconciled from 'reconciled';

const reconciler = reconciled({
	createNode: type => document.createElement(type),
	createTextNode: text => document.createTextNode(text),
	setTextNodeValue: (node, text) => (node.textContent = text),
	appendNode: (parentNode, childNode) => parentNode.appendChild(childNode),
});

const app = reconciler.create(document.body);
app.render(<h1>Stranger Things</h1>);
app.unmount();

React itself doesn't require a certain environment to run. In simple terms, it only manages components and updates. Then, renderer takes representation of this component tree and displays it somewhere. For example, every React app in the browser uses react-dom renderer. react-native lets you build mobile native apps with React. Ink renders your React app in the terminal. There's even react-360 renderer for building VR apps.

Custom React renderers let you render React apps anywhere you want, as long as you can build a custom renderer for it. This is where reconciled comes in. There's not a lot of documentation around building custom renderers, so I extracted all my knowledge of building them for Ink into a simple-to-use module. Enjoy.

I think reconciled is a good first step in learning how to make a React renderer. If you notice that reconciled is too limited for your use case, I'd recommend checking out its source code and building your renderer without using reconciled.

Create a reconciler with the specified config for your custom renderering. Returns a reconciler object. Reconciler is a set of methods that let you synchronize React's state with your custom output (see example above).

Type: object

Methods for manipulating nodes.

Create a new node.

Type: string

Name of the node that's being rendered. When rendering <h1>, type equals 'h1'.

Type: object

Props to add to the node. When rendering <input value="abc"/>, props equals { value: 'abc' }.

Example implementation:

const createNode = (type, props) => {
	const node = document.createElement(type);

	for (const [key, value] of Object.entries(props)) {
		node.setAttribute(key, value);
	}

	return node;
};

Learn more:

• document.createElement()
• Element.setAttribute()

Create a new text node. For example, when rendering <h1>Hello World</h1>, a text node will be created where text equals 'Hello World'.

Type: string

Value of text node.

Example implementation:

const createTextNode = text => document.createTextNode(text);

Learn more:

• document.createTextNode()

Update value of a text node.

Type: any

Text node to update.

Type: string

Text to update in a text node.

Example implementation:

const setTextNodeValue = (node, text) => {
	node.textContent = text;
};

Learn more:

• Node.textContent

Insert a new node to parent node as the last child.

Type: any

Parent node to append child node into.

Type: any

Child node to append.

Example implementation:

const appendNode = (parentNode, childNode) => {
	parentNode.appendChild(childNode);
};

Learn more:

• Node.appendChild()

Insert a new node before a certain child node.

Type: any

Parent node to insert child node into.

Type: any

Node to insert.

Type: any

Node used for reference, so that new node is inserted before this one.

Example implementation:

const insertBeforeNode = (parentNode, newChildNode, beforeChildNode) => {
	parentNode.insertBefore(newChildNode, beforeChildNode);
};

Learn more:

• Node.insertBefore()

Update node with new props.

Type: any

Node to update.

Type: object

Set of old props. Compare newProps to this object to figure out which props were removed.

Set of new props.

Example implementation:

const updateNode = (node, oldProps, newProps) => {
	for (const key of Object.keys(oldProps)) {
		if (newProps[key] === undefined) {
			node.removeAttribute(key);
		}
	}

	for (const [key, value] of Object.entries(newProps)) {
		node.setAttribute(key, value);
	}
};

Learn more:

• Element.removeAttribute()
• Element.setAttribute()

Remove child node from parent node.

Type: any

Parent node.

Type: any

Child node.

Example implementation:

const removeNode = (parentNode, childNode) => {
	parentNode.removeChild(childNode);
};

Learn more:

• Node.removeChild()

Callback which is called after every change is completed by the reconciler. Useful for renderers like Ink, which have to build custom output for environment that renderer is built for. In Ink's case, it's terminal, so there's no DOM like in the browser. Use this callback as an indication that there has been a change and UI needs to be updated.

Type: object

Update current node tree with a new node and its children.

Type: JSX.Element

New node to replace the current one with.

Example:

reconciler.render(<h1>Hello Mind Flayer</h1>);

Unmount entire node tree and remove all nodes.