Dead simple form library for React/Preact.

Mu-forms stores form data in the state of a wrapper Component (<Form>) instead of a Redux store. By doing so, it keeps invalid / incomplete user-submitted data out of your store. Leaving it cleaner and easier to reason about. At the same time it allows you to connect to the data of the parent <Form> by creating connected components using connectForm.

Mu-forms additionally provides validation, synchronous and asynchronous submission, as well as the ability to preload the form with data.

mu-forms can be installed from npm:

npm install mu-forms --save

or using Yarn:

yarn add mu-forms

To include it in a Preact project, import from mu-forms/preact like so:

import { Form, connectForm } from 'mu-forms/preact'

Similarly to use it for React based projects, import from mu-forms/react

import { Form, connectForm } from 'mu-forms/react'

Check the examples to see working code in both React and Preact.

Creating a form is as simple as adding connected inputs and giving them a name prop. In the following example, TextInput is a wrapper arround an input, and Errors just displays any errors we might have.

<Form onSubmit={submit} onSubmitted={done}>
	<Errors /> 
	<h1> Example Registration Form </h1>

	<TextInput
		label="Email"
		name="email"
		type="email"
		required
	/>

	<TextInput
		label="Password"
		name="password"
		type="password"
		minLength={8}
		invalidText="Please enter at least 8 characters"
		required
	/>

	<TextInput
		label="Confirm Password"
		name="password2"
		type="password"
		validate={(val, form) => val == form.password }
		invalidText="Passwords must match"
		required
	/>
	<button type="submit"> 
		<span>Register</span>
		<span className="loading" />
	</button>
</Form>

The submit function shown above can return a Promise in order to put the form into a submitting state.

function submit(data) {
	// return a promise to show the loading state of the form.
	return new Promise((resolve,reject) => {
		setTimeout(() => {
			if (data.email == 'error@example.com') {
				// this will set `status.error` to true, and display the error
				reject('Oops Something went wrong...');
			} else {
				// this will call our `onSubmitted` function.
				resolve();
			}
		}, 2400);
	});
}

The done function will only be fired if the submit was successful. Normally you would use this for closing a modal, or navigation, but we will just use an alert to show that it has completed.

function done(result) {
	alert('Form successfully submitted');
}

To make the above example actually work, we need to create components that can be connected into the form. We will start with a text input wrapper.

/** 
 * This component wraps a standard `input` with a label, and some optional invalid text 
 * invalid text is shown/hidden using css, but you could use `invalid` and `status.invalid` instead
 */
const _TextInput = ({ invalid, invalidText, onChange, validate, label, status, ...props}) => (
	<label className="text-input" invalid={invalid ? '' : null}>
		<span className="text-input__label">{label}</span>
		<input onInput={onChange} {...props}/>
		<span className="text-input__invalid_text">{invalidText}</span>
	</label>
);
const TextInput = connectForm(_TextInput);

/* This component displays any errors present on the form */
const _Errors = ({ status }) => (
	status.error ? (
		<div className="error">
			<span className="error-title">Error:</span>
			<span>{status.error}</span>
		</div>
	) : null
)
const Errors = connectForm(_Errors);

Mu-forms provides access to the native HTML5 input validation. connectForm passes the invalid prop to the connected component, which can be used to change the class or display messaging. The invalid property reflects the native HTML5 input validity based on required, pattern, etc. including custom HTML5 validity. Mu-forms provides the ability to set custom validation by passing a validate function to your connected form field. The validate function gets passed three arguments.

• value - The value of the current field.
• data - The complete current form data.
• name - The name of the current field. (useful if you use one function for multiple fields).

The validate function just has to return a boolean, and mu-forms will set the native custom validity for you.

Mu-forms will only call the onSubmit property of the <Form> component once all the validations have been met. If submission is attempted and the form is still invalid, the form element is marked with the invalid attribute, and status.invalid is set to true until all inputs become valid again. onSubmit gets called with two arguments:

• data - The complete form data.
• form - The underlying html form element.

onSubmit may return a Promise in which case the form will be marked with the submitting attribute and status.submitting will be set to true until the Promise either resolves or rejects.

• If the promise resolves, onSubmitted is called with the resolved value.
• If the promise rejects, status.error is set to the error value returned from the promise.
• If onSubmit does not return a promise, onSubmitted is called immediately with whatever value onSubmit returned as it's only argument.

With this behavior, it is easy to style the form so that invalid inputs only show as invalid once the user has attempted to submit.

form[invalid] .invalid { 
	color : red 
} 

You can also easily integrate with an asynchronous method of submitting the data such as fetch, while showing a loading state to the user. The loading state can either be toggled using connectForm and listening to status.submitting, or by showing the loading spinner with css like so:

.spinner {
	display: none;
}
form[submitting] .spinner {
	display: block;
}

Error states can also easily be handled by simply rejecting the promise with a value that you can later use to generate a user friendly message. You can simply create an error component and connect it to the form with connectForm. As soon as the Promise returned by onSubmit becomes rejected, status.error will be updated with error value caught by the Promise.

• Form
• onChange
• onSubmit
• onSubmitted
• connectForm

src/common/form.js:35-170

Extends Component

The <Form> component will store the data from any connected inputs. It will call onSubmit if the form is submitted (user presses enter, or clicks on a submit button), and is valid, onSubmit is called with two arguments: data and form.

Parameters

• props Object
  • props.onChange onChange
  • props.onSubmit onSubmit
  • props.onSubmitted Function
  • props.initialState Object
• context

src/common/form.js:102-119

The function passed to onChange will be called whenever the form data is updated.

Parameters

• data Object An Object containing the complete form data.
• valid Boolean a Boolean set to true if all the form elements are valid.

src/common/form.js:102-119

The function passed to onSubmit will be called when the form is submitted, and all validations have been met.

Parameters

• data Object An Object containing the complete form data
• form Element The underlying form element

Examples

// post data to external api as JSON
(data) => fetch({ 
   method : 'post',
   url    : '/api/update/my/thing',
   body   : JSON.stringify(data),
}).then(r => {
   // any 2XX status will return the JSON data to `onSubmitted`
   if (r.ok) return r.json();

   // status.error will be set with the JSON value returned for this error
   return r.json().then(body => Promise.reject(body));
})

(data) => promise.reject('Closed for Business')

Returns (Promise | Object | String | Number | Boolean | undefined) If onSubmit returns a Promise, the form is marked as submitting until the promise either resolves or rejects.- If the promise resolves, onSubmitted is called with the value returned from the promise.

• If the promise rejects, status.error is set to the error value returned from the promise.If onSubmit does not return a Promise, onSubmitted is immediately called. onSubmitted has only one argument, which is the value returned from onSubmit.

src/common/form.js:102-119

The function passed to onSubmitted will be called once the submission is considered complete. That is, either after the onSubmit has completed synchronously, or after a promise returned by onSubmit has resolved.

Parameters

• value (Object | String | Number | Boolean | undefined) The value returned by onSubmit synchronously, or returned by a Promise asynchronously.

src/common/connect.js:87-122

Wire up a component to the <Form>, giving it access to form data as status. If the connected component is passed a name property, then the component also gets the value, invalid and onChange properties.

If the name property is present, a form element with the same name must be included inside the form. This is required in order to use the native HTML5 validity. If you are not using an input element as part of the UI, it is perfectly acceptable to create a display: none input that simply reflects the same validity. for example:

<input value={value} style={{ display : 'none' }} {...props} />

Note: the input only needs to reflect the same validity, so if you are only concerned with required for instance, you can store a complex (non-string) value in the state, while simply storing a placeholder in the input (for example: value={value == undefined ? '' : '__NOT_EMPTY__' })

onChange(e) is a function which expects a change or input event from a native HTML element. If you need to pass it data in a different format, you can use mapEvent to change the data into the correct format.

Parameters

• Child Component Component to be wrapped
• mapEvent (String | Function) (Optional) maps the input to onChange to the value to be stored. - String arguments are treated as a . delimited path.
  • Functions are passed the argument to onChange, and the result is stored in state.

Examples

// view only
const _Debug = (props) => (
    <pre>{JSON.stringify(props, null, 4)}</pre>
); 
const Debug = connectForm(_Debug);
<Form>
    <Debug />
    ....
</Form>

// Wrapped input
const _Input = ({ status, onChange, invalid, className, ...props }) => (
    <input 
        className={invalid ? 'invalid ' + className : className}
        onInput={onChange}
        {...props} 
    />
);
const Input = connectForm(_Input);

<Form onSubmit={(data) => console.log(data)}>
    <Input name="test" required />
    <button type="submit">Submit</button>
</Form>

Returns Component ConnectedComponent