Package Exports

formalities

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (formalities) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

Formalities

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

Formalities makes use of Immer and Immutable State Controller to create immutable state updates.

Install

npm install formalities

The case for Formalities

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

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

const INITIAL_STATE: MyFormState = {}

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

    function onChangeName(evt: React.ChangeEvent<HTMLInputElement>) {
        setName(evt.target.value)
    }

    function onChangeAge(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)
        }
    }

    function onChangeAddress(evt: React.ChangeEvent<HTMLInputElement>) {
        setAddress(evt.target.value)
    }

    return (
        <div>
            <h1>Existing</h1>
            <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>
            <h2>Output</h2>
            <div>Name: {name}</div>
            <div>Age: {age}</div>
            <div>Address: {address}</div>
        </div>
    )
}

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

Examples

Component state

Using the hook useController we create a 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 { useController, Formalities } from 'formalities'

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

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

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

Formalities's useController 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.

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 = useController(props.value, 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) {
    function onChange(evt: React.ChangeEvent<HTMLInputElement>) {
        props.setValue(evt.target.value)
    }

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

}

export default wrapComponent(MyTextField)

The last line above uses Formalities's to wrap MyTextField, which accepts props value and setValue, 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 = useController(...)

    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 setValue 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.