React Hook useForm

useForm provides an interface around an object for use in forms.

Install

npm install --save @caesium/hook-use-form

Usage

The best useForm experiance comes when using Typescript.

Lets say you want to collect a users name and email for a newsletter form.

const NewsletterSignUp: React.FunctionComponent = () => {
  const {formBind, bind, onSubmit} = useForm({
    name: '',
    email: ''
  })

  onSubmit((data) => {
    // `data` is the forms state when it was submitted
    doSignup(data.name, data.email)
  })

  return <form {...formBind()}>
    <input {...bind('name')} />
    <input {...bind('email')} />
    <input type="submit" value="Sign Up!" />
  </Form>
}

useForms output is an object with this structure:

property	type	value
bind	(field: keyof T) => {value, onChange, name}	Used to bind to a single field.
clear	() => void	Function that sets the form back to its initial value.
controlledInput	(fieldName: keyof T) => ControlledInput	Function that is used to create input fields (See Creating your own input).
data	T	The current state of the form.
formBind	() => {onSumbit}	Used to bind a forms submit action to useForm
onSubmit	(handler: (data: T) => void) => void	A function which takes a callback to be used when the form is submitted.
validate	(field: keyof T, validator: (value: any) => boolean) => void	A function that takes the field name and validation function as arguments.
valid	(field?: keyof T) => boolean	A function that checks the validity of one field or the whole form and returns a boolean value.
set	(data: T) => void	Function to set the data to a given value. Useful if you want to use one form to edit multiple entries.
label	`(field: keyof T) => {for}	Returns the fields label for.
changed	(field?: keyof T) => boolean	Has the given field, or any field changed from the intial data.
submit	() => void	Submit the form.
meta	Meta	The meta data set in options.

Meta Data

You can optionally store meta data in the form state by passing a meta object in options.

const MyForm = () => {
  const {formBind, meta, bind, onSubmit, set} = useForm({
    name: ''
  }, {meta: {userId: 0}})

  onSubmit(({name}, {userId}) => {
    if(userId === 0){
      newUser(name)
    }else{
      updateUser(userId, name)
    }
  })

  return <div>
    <form {...formBind()}>
      <b>{meta.userId === 0 ? 'Creating user' : 'Editing user'}</b>
      <input {...bind('name')}>
    </form>
    <button onClick={() => {
      set({name: 'First User'}, {userId: 1})
    }}>Edit User 1</button>
    <button onClick={() => {
      set({name: 'Second User'}, {userId: 2})
    }}>Edit User 2</button>
  </div>
}

meta can then be updated through the second parameter of set. This allows you to store additional state with your form instead of using useState in your own components.

meta is passed to your submit handler as the second argument.

Validation

Validating fields with useForm is easy. Going back to the earlier example, lets ensure that the email contains an @

const NewsletterSignUp: React.FunctionComponent = () => {
  const {valid, bind, formBind, validate} = useForm({
    name: '',
    email: ''
  })

  validate('email', (value) => {
    return value.indexOf('@') > -1
  })

  return <form {...formBind()}>
    <input {...bind('name')} style={{color: valid('name') ? '#000' : '#f00'}} />
    <input {...bind('email')} style={{color: valid('email') ? '#000' : '#f00'}} />
    <input type="submit" value="Subscribe" disabled={!valid()} />
  </form>
}

Creating your own input

Sometimes simply using bind wont work as your not using and input and you want to have a custom input.

useForm returns a function of controlledInput which gives more control over a single field.

controlledInput returns the following:

property	type	value
field	keyof T	The current field
value	T[field]	The current value (connected to state)
update	(newValue: T[field]) => void	Change the value to the supplied value
valid	() => boolean	Returns a boolean value for the fields current validity
bind	{value, onChange, name}	The same as if you had called bind(field) directly from useForm
id	string	The id of the input.