Formalities

A small package to build React forms with immutable state, type-safety and not a lot of boilerplate.

Formalities makes use of empire-state-react to create immutable state updates.

You'll want to familiarise yourself with empire-state-react and empire-state before using this package.

Install

npm install formalities

Usage

import { useNewController, useSnapshot, Formalities } from 'formalities'

function MyForm() {
	const controller = useNewController({
		name: '',
		age: undefined as number | undefined,
		address: '',
	})

	const handleSave = useCallback(function(evt: React.MouseEvent) {
		evt.preventDefault()

		const value = controller.value
		// send the value to the server
	}, [controller])

	return (
		<div>
			<div>
				<label>Name:</label>
				{/* Note that VS Code will autocomplete and type-check the prop attribute */}
				<Formalities.Text type="text" controller={controller} prop="name" />
			</div>
			<div>
				<label>Age:</label>
				<Formalities.Number type="number" controller={controller} prop="age" updateOnBlur={true} />
			</div>
			<div>
				<label>Address:</label>
				<Formalities.Text type="text" controller={controller} prop="address" />
			</div>
			<button onClick={handleSave} />
		</div>
	)
}

Components

• <Formalities.Text> an <input> element for string properties
• <Formalities.Number> an <input> element for number properties
• <Formalities.Checkable> an <input> element for checkboxes
• <Formalities.MultiCheckable> an <input> element for checkboxes for array properties
• <Formalities.TextArea> a <textarea> element for string properties
• <Formalities.Select> a <select> element
• <Formalities.Indexed> a component for custom array properties

See the examples for examples of using each of these components.

The case for Formalities

This is how we might manage form state in React components, while maintaining type-safety with TypeScript:

function MyForm() {
	const [name, setName] = useState<string | undefined>(undefined)
	const [age, setAge] = useState<number | undefined>(undefined)
	const [address, setAddress] = useState<string | undefined>(undefined)

	const onChangeName = useCallback(function(evt: React.ChangeEvent<HTMLInputElement>) {
		setName(evt.target.value)
	}, [])

	const onChangeAge = useCallback(function(evt: React.FocusEvent<HTMLInputElement>) {
		const newAge = parseInt(evt.target.value, 10)
		if (isNaN(newAge)) {
			evt.target.value = age !== undefined ? `${age}` : ''
			evt.target.select()
		} else {
			setAge(newAge)
		}
	}, [])

	const onChangeAddress = useCallback(function(evt: React.ChangeEvent<HTMLInputElement>) {
		setAddress(evt.target.value)
	}, [])

	return (
		<div>
			<div>
				<label>Name:</label>
				<input type="text" value={name || ''} onChange={onChangeName} />
			</div>
			<div>
				<label>Age:</label>
				<input type="number" defaultValue={age !== undefined ? `${age}` : ''} onBlur={onChangeAge} />
			</div>
			<div>
				<label>Address:</label>
				<input type="text" value={address || ''} onChange={onChangeAddress} />
			</div>
		</div>
	)
}

And we could be using immer so we have immutable state, but that's even more boiler-plate.

Examples

Component state

Using the hook useNewController we create a new Controller that reads and updates from the component's state.

In the component we use the Formalities components to create normal <input> elements, but bound to the value of one of the Controller's properties, and reporting changes back to the component state.

The Formalities components supports all of the regular <input> properties.

import { useNewController, Formalities } from 'formalities'

interface MyFormState {
	name: string
	age?: number
	address: string
}

function MyForm() {
	const controller = useNewController<MyFormState>({
		name: '',
		address: '',
	})

	return (
		<div>
			<div>
				<label>Name:</label>
				<Formalities.Text controller={controller} prop="name" />
			</div>
			<div>
				<label>Address:</label>
				<Formalities.Text controller={controller} prop="address" />
			</div>
		</div>
	)
}

useNewController returns a Controller with an initial value. The type of the Controller is determined from that initial value.

The <Formalities.Text> component specifies the Controller instance via the controller prop, and which property inside the controller via the prop prop. Due to the type-safety of the Controller the prop prop can only accept appropriate value, and VS Code will autocomplete valid prop values for you.

Component props

Not all components manage their own state. Many components use props to receive state and to report changes.

In this next example the component is a part of a form, reporting changes back to its parent component via the onChange function in its props. The controller uses the value and onChange properties from the props to handle this automatically for you.

interface MyFormSectionContents {
	givenName?: string
	familyName?: string
}

interface MyFormSectionProps {
	onChange: (newValue: MyFormSectionContents) => void
	value: MyFormSectionContents
}

function MyFormSection(props: MyFormSectionProps) {
	const controller = useSnapshotController({ value: props.value, change: props.onChange })

	return (
		<div>
			<div>
				<label>Full name:</label>
				<Formalities.Text controller={controller} prop="givenName" placeholder="Given name" />
				<Formalities.Text controller={controller} prop="familyName" placeholder="Family name" />
			</div>
		</div>
	)
}

Custom components

In the examples above we've used Formalities's <Formalities.String> component replacement for the standard <input> element. You can also create your own components that interact with the controller:

import { Snapshot, wrapComponent } from 'formalities'

interface MyTextFieldProps extends Snapshot<string> {}

function MyTextField(props: MyTextFieldProps) {
	const { value, change } = props

	const onChange = useCallback(function(evt: React.ChangeEvent<HTMLInputElement>) {
		change(evt.target.value)
	}, [change])

	return (
		<div>
			<input type="text" value={value} onChange={onChange} />
		</div>
	)
}

export default wrapComponent(MyTextField)

The last line above uses Formalities's to wrap MyTextField, which accepts props value and change, to create a component that instead accepts props controller and prop.

It can then be used like <Formalities.Text> in the examples above, as in:

import MyTextField from './MyTextField'

function MyForm() {
	const controller = useNewController(...)

	return (
		<div>
			<div>
				<label>Name:</label>
				<MyTextField controller={controller} prop="name" />
			</div>
			<div>
				<label>Address:</label>
				<MyTextField controller={controller} prop="address" />
			</div>
		</div>
	)
}

Now when the MyTextField component wants to change its value, it calls the change function in its props, which invokes the controller, which updates the state on the MyForm component, triggering React to update, which updates the form.

More examples

See the packages/examples directory for more examples.