Formts

Type-safe, declarative and performant React form & validation library

Status

A stable release has been reached. Further development of new features is currently not planned. Bug fixes will be provided if needed, feature requests wil still be considered.

Features

• Fully type-safe API, purpose built to get the most out of Typescript type-inference
• Declarative definition of form shape and validation rules
• Runtime type-checking of form values against the schema
• Convenient hooks & context based API allowing for isolated re-renders
• Plain react-typescript, 0 dependencies
• View layer agnostic - no components are provided, works with any 3rd-party components
• handleChange function for dealing with change events automatically
• Advanced validation API which enables:
  • specifying dependencies on other fields
  • specifying validation triggers for individual rules
  • selective validation of just the affected fields on value changes
  • separation of error messages from error codes (optional)
  • async validation rules with debounce option
  • easy mixing of built-in rules with custom functions
  • combining multiple validation rules into composite validators
• Good scalability for very large and complex forms

Getting Started

1) Install

npm install @virtuslab/formts
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2) Define shape of the form

import { FormSchemaBuilder, FormFields } from "@virtuslab/formts";

const Schema = new FormSchemaBuilder()
  .fields({ answer: FormFields.string() })
  .errors<string>()
  .build();
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3) Define validation rules (optional)

import { FormValidatorBuilder } from "@virtuslab/formts";

const validator = new FormValidatorBuilder(Schema)
  .validate(
    Schema.answer,
    val => (val === "" ? "Required!" : null),
    val => (val !== "42" ? "Wrong answer!" : null)
  )
  .build();
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3) Create controller holding form state

import { useFormController, FormProvider } from "@virtuslab/formts";

const MyForm: React.FC = () => {
  const controller = useFormController({ Schema, validator });

  return (
    <FormProvider controller={controller}>
      <AnswerField />
      <FormActions />
    </FormProvider>
  );
};
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4) Connect inputs to form

import { useField } from "@virtuslab/formts";

const AnswerField: React.FC = () => {
  const field = useField(Schema.answer);

  return (
    <section>
      <label htmlFor={field.id}>
        What is the answer to the meaning of life, the universe, and everything?
      </label>
      <input
        id={field.id}
        value={field.value}
        onChange={field.handleChange}
        onBlur={field.handleBlur}
      />
      <div className="error">{field.error}</div>
    </section>
  );
};
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5) Connect actions to form

import { useFormHandle } from "@virtuslab/formts";

const FormActions: React.FC = () => {
  const form = useFormHandle(Schema);

  return (
    <section>
      <button
        type="submit"
        disabled={form.isValid === false}
        onClick={() => form.submit(console.log)}
      >
        Submit!
      </button>

      <button type="reset" onClick={form.reset}>
        Reset
      </button>
    </section>
  );
};
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Documentation

Currently API documentation is available in form of:

• exhaustive JSDocs
• TYPEDOC docs
• CodeSandbox examples

Examples

Play around with the code on CodeSandbox to learn Formts API and features:

a) Step-by-step introduction:

1. basic form (naive)
2. basic form + optimized re-renders
3. basic form + validation
4. basic form + Material-UI

b) HTML input bindings:

1. radio group input
2. checkbox group input
3. select input
4. input array
5. mui multi-select input
6. mui date-picker input

c) Advanced examples:

1. change password form
2. order pizza form
3. form with summary of validation errors
4. registration stepper form

Why another form lib?

Update 2023:

Some of the reasons outlined below are no longer valid as react-hook-form has improved since this project started. It offers good type-safety and performance. If for some reason you are not happy with it however, this library offers different approach to many aspects of form management and a powerful validation API - so it may suit your needs better.

a) Type-safety

Most popular form libraries like Formik and react-hook-form are written in Typescript but are not designed with type-safe API as a primary concern.

There is some evidence that this is important for some people:

• Reddit: Fully type-safe form libraries?
• Formik issue: Strongly Typed Fields
• react-hook-form extension: strictly-typed

There are some existing truly type-safe react form solutions, but each has a costly dependency associated with it:

• formstate --> MobX
• Typescript.fun --> fp-ts
• ReForm --> ReasonML

b) Performance

There are SOME form libraries with really good performance (react-hook-form). However combining convenient Context based hook API with React performance optimizations is still problematic. See https://react-hook-form.com/advanced-usage#FormProviderPerformance for example.

c) Declarative validation API

Usually form libs "outsource" advanced validation to schema-based libraries such as Yup. This seems like a great idea but has some limitations:

• yup and similar packages are not designed with type-safety in mind
• Advanced optimizations (such as validating only the affected fields rather than the entire form) are not available.

Limitations

• Form values type is limited by schema definition API and can't represent more advanced TS types
• Adding required validator does not impact type of values.
• number() fields are typed as number | "", this is because HTML number inputs work with "" as empty value.
• Definition of form shape and validation split into 2 separate steps
• Binding to input components is more verbose than with other form libraries (this is intentional to keep API type-safe and view-layer agnostic)