react-form-with-constraints

Simple form validation for React in ~400 lines of code

• Installation: npm install react-form-with-constraints
• CDN: https://unpkg.com/react-form-with-constraints/dist/

Introduction: what is HTML5 form validation?

<form>
  <label for="email">Email:</label>
  <input type="email" id="email" required>
  <button>Submit</button>
</form>

The required HTML5 attribute specifies that the user must fill in a value, type="email" checks that the entered text looks like an email address.

Resources:

• Making Forms Fabulous with HTML5
• Constraint Validation: Native Client Side Validation for Web Forms
• MDN - Form data validation
• MDN - Form input types

What react-form-with-constraints brings

• Minimal API and footprint
• Control HTML5 error messages: <FieldFeedback when="valueMissing">My custom error message</FieldFeedback>
• Custom constraints: <FieldFeedback when={value => ...}>
• Warnings and infos: <FieldFeedback ... warning>, <FieldFeedback ... info>
• No dependency beside React (no Redux, MobX...)
• No special component like <TextField>, just plain old <input> or whatever you like
• Re-render only what's necessary
• ...

<input type="password" name="password"
       value={this.state.password} onChange={this.handleChange}
       required pattern=".{5,}" />
<FieldFeedbacks for="password" show="all">
  <FieldFeedback when="valueMissing" />
  <FieldFeedback when="patternMismatch">
    Should be at least 5 characters long
  </FieldFeedback>
  <FieldFeedback when={value => !/\d/.test(value)} warning>
    Should contain numbers
  </FieldFeedback>
  <FieldFeedback when={value => !/[a-z]/.test(value)} warning>
    Should contain small letters
  </FieldFeedback>
  <FieldFeedback when={value => !/[A-Z]/.test(value)} warning>
    Should contain capital letters
  </FieldFeedback>
  <FieldFeedback when={value => !/\W/.test(value)} warning>
    Should contain special characters
  </FieldFeedback>
</FieldFeedbacks>

Examples

• CodePen basic example: https://codepen.io/tkrotoff/pen/BRGdqL
• CodeSandbox Bootstrap 4 example: https://codesandbox.io/s/qk0zro1qm4
• CodeSandbox WizardForm example: https://codesandbox.io/s/my0ojyzq6p
• CodeSandbox SignUp example: https://codesandbox.io/s/62qwozvm0k
• CodeSandbox ClubMembers example: https://codesandbox.io/s/q8364yn60j

Other examples inside the examples directory.

How it works

The API works the same way as React Router v4:

<Router>
  <Route exact path="/" component={Home} />
  <Route path="/news" component={NewsFeed} />
</Router>

It is also inspired by AngularJS ngMessages.

If you had to implement validation yourself, you would end up with a global object that tracks errors for each field. react-form-with-constraints works similarly (although not using setState). It uses React context to share the FieldsStore object across FieldFeedbacks and FieldFeedback.

API

The API reads like this: "for field when constraint violation display feedback", example:

<FieldFeedbacks for="password">
  <FieldFeedback when="valueMissing" />
  <FieldFeedback when="patternMismatch">Should be at least 5 characters long</FieldFeedback>
</FieldFeedbacks>

for field "password"
  when constraint violation "valueMissing"    display "the HTML5 error message (*)"
  when constraint violation "patternMismatch" display "Should be at least 5 characters long"

(*) element.validationMessage

• FieldFeedbacks

  • for: string => refer to a name attribute (e.g <input name="username">), should be unique to the current form
  • show?: 'first' | 'all' => display the first error/warning encountered (default) or all of them

  Note: you can place FieldFeedbacks anywhere and have as many as you want for the same field

• FieldFeedback

  • when: ValidityState string | '*' | function => HTML5 constraint violation name or a callback
  • error?: boolean => treat the feedback as an error (default)
  • warning?: boolean => treat the feedback as a warning
  • info?: boolean => treat the feedback as an info

• FormWithConstraints

  • validateFields(...inputsOrNames: Array<Input | string>): void => should be called when a field changes or the form is submitted, will re-render the proper FieldFeedbacks
  • isValid(): boolean

Browser support

You can use HTML5 attributes like type="email", required, pattern..., in this case a recent browser is needed,...

<label htmlFor="username">Username</label>
<input type="email" name="username" id="username"
       value={this.state.username} onChange={this.handleChange}
       required />
<FieldFeedbacks for="username">
  <FieldFeedback when="*" />
</FieldFeedbacks>

...or ignore them and rely on when functions:

<label htmlFor="username">Username</label>
<input name="username" id="username"
       value={this.state.username} onChange={this.handleChange} />
<FieldFeedbacks for="username">
  <FieldFeedback when={value => value.length === 0}>Please fill out this field.</FieldFeedback>
  <FieldFeedback when={value => !/\S+@\S+/.test(value)}>Invalid email address.</FieldFeedback>
</FieldFeedbacks>

In the last case you will have to manage translations yourself.

react-form-with-constraints, like React 16, depends on the collection types Map and Set. If you support older browsers (<IE11) you will need a global polyfill such as core-js or babel-polyfill.

Notes

• A readonly or disabled input won't trigger any HTML5 form constraint like required.
• With <input type="number"> it's better to use onInput instead of onChange, see https://github.com/facebook/react/issues/11142