Empire State - Forms

A small package to build React forms with immutable state, limited re-rendering, type-safety and no boilerplate.

empire-state-forms 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 empire-state-forms

Usage

import { useControllerWithInitialState, useControllerValue, Text, Number } from 'empire-state-forms'

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

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

		const value = controller.value
		// now send the value to the server or parent component
	}, [controller])

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

Components

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

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

The case for empire-state-forms

Here is a comparison to the code sample above with how we might normally 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>
	)
}

There's a lot more code, and complex code, to deal with. And we could be using immer so we have immutable state, but that's even more boilerplate.

Examples

useControllerWithInitialState

Using the hook useControllerWithInitialState we create a new Controller with an initial state. Changes to the controllers value do not cause the component to re-render.

In the component we use the empire-state-forms 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 empire-state-forms components supports all of the regular <input> properties.

import { useControllerWithInitialState, Text } from 'empire-state-forms'

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

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

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

useControllerWithInitialState returns a Controller with an initial value. The type of the Controller is determined from that initial value, or you can specify the type, e.g. useControllerWithInitialState<Type>(...).

The <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. If the controller itself contains the value you want to use, omit the prop prop.

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 = useStatelessController(props.value, props.onChange)

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

Custom components

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

import { Snapshot, wrapComponent } from 'empire-state-forms'

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 empire-state-forms'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 <Text> in the examples above, as in:

import MyTextField from './MyTextField'

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

	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 updates the controller.

More examples

See the examples for more examples.