skeleform

Form management and validation toolkit originally a part of https://github.com/prototypdigital/skeletor

Usage

Handle form value updates and validation with useForm. Full TypeScript support, ability to configure optional parameters, custom validation rules.

Flexible in its function, supports multiple validation approaches through callbacks:

1. For on-change validation, use update("prop", value, true)
2. To trigger standalone validation, use validate("prop")
3. Validate entire form with validateForm()

The order of importance when it comes to validating fields is:

1. Custom validation rule - will get the value as-is for your rule to validate it fully. The configuration rule receives the current value, state and optional flag values for you to validate against.
2. If there is no custom validation rule and the primitive value check returns false (there is no value), check if the field is optional. If optional, the validation result is true, otherwise it is false;
3. If all previous checks have not been triggered, return the primitive "has value" check result. This will return false for values such as: null | undefined | NaN | "" | Invalid Date. This will return true if you have a complex value type such as object | Array, so in case you have a complex value type use a custom validation rule to get what you need.

Example 1: Simple use case with standalone validation on blur:

const {state, validation, update, validate} = useForm({email: "", password: "");

...
<input
  ...
  value={state.email}
	onChange={(e) =>  update("email", e.currentTarget.value)}
	onBlur={() => validate("email")}
/>
...

Example 2: Simple use case with on-change validation:

// See example 1
...
onChange={(e) =>  update("email", e.currentTarget.value, true)}
...

Example 3: Simple use case with on-submit validation:

// See example 1

function submit() {
	if(!validateForm()) {
		// Throw invalid error
		// validation object will be populated
	}
}

...
<input
  ...
	value={state.email}
	onUpdate={(e) =>  update("email", e.currentTarget.value)}
/>
<button onPress={submit}>Submit</button>

Validation has three possible values:

1. undefined = validation of the field value has not been done yet.
2. false = validation has failed, the state value is not considered valid.
3. true = validation has succeeded, the state value is considered valid.

What does that mean? Well, it means that when you have validation.email === false, you should show an error message on the field. undefined | true are not relevant for rendering, only functionally to block form submit events.

Example 4: Form configuration

const { state, validation, update, validate } = useForm(
{ firstName: "", middleName: "", lastName: ""},
{
	// If left empty, validation.middleName will be true
	optional: ["middleName"],
	// validation.lastName is invalid if lastName is <3 characters long
	// state can be used to compare with other values (ie repeat password)
	rules: { lastName: (value, state, optional) => value.length >= 3,
}

Example 5: useFormUtils

Utility functions to help with standalone state validation, such as when re-validating a list of form values in a parent components.

const { stateValidation } =  useFormUtils<Person>();

function validatePeople() {
	return people.every(person => stateValidation(person).valid);
}

Other utilities: doesValueExist, validateByRule, isOptional, fieldValidation, stateValidation. Some are meant for internal useForm usage, such as fieldValidation and validateByRule, but are not unusable.