React-form-with-constraints NPM

react-form-with-constraints

Simple form validation for React

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

Check the changelog for breaking changes and fixes between releases.

Introduction: what is HTML5 form validation?

⚠️ Client side validation is cosmetic, you should not rely on it to enforce security

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

input required input type="email"

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:

What react-form-with-constraints brings

Minimal API and footprint
Unobtrusive: easy to adapt regular React code
Control HTML5 error messages: <FieldFeedback when="valueMissing">My custom error message</FieldFeedback>
Custom constraints: <FieldFeedback when={value => ...}>
Warnings and infos: <FieldFeedback ... warning>, <FieldFeedback ... info>
Async validation
No dependency beside React (no Redux, MobX...)
Re-render only what's necessary
Easily extendable
Support for React Native with npm package react-form-with-constraints-native
Bootstrap 4 styling with npm package react-form-with-constraints-bootstrap4
Material-UI integration with npm package react-form-with-constraints-material-ui
...

<input type="password" name="password"
       value={this.state.password} onChange={this.handleChange}
       required pattern=".{5,}" />
<FieldFeedbacks for="password">
  <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>
</FieldFeedbacks>

Examples

CodePen basic example: https://codepen.io/tkrotoff/pen/BRGdqL
CodeSandbox Bootstrap 4 example: https://codesandbox.io/s/nkqrr17qqj
CodeSandbox Material-UI example: https://codesandbox.io/s/zx62rw4k64
CodeSandbox WizardForm example: https://codesandbox.io/s/my0ojyzq6p
CodeSandbox SignUp example: https://codesandbox.io/s/62qwozvm0k
CodeSandbox ClubMembers example: https://codesandbox.io/s/q8364yn60j
React Native example:
iOS Android

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. 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

Async support works as follow:

<FieldFeedbacks for="username">
  <Async
    promise={checkUsernameAvailability} /* Function that returns a promise */
    then={available => available ?
      <FieldFeedback key="1" info style={{color: 'green'}}>Username available</FieldFeedback> :
      <FieldFeedback key="2">Username already taken, choose another</FieldFeedback>
      // Why key=*? Needed otherwise React gets buggy when the user rapidly changes the field
    }
  />
</FieldFeedbacks>

Trigger validation:

class MyForm extends React.Component {
  async handleChange(e) {
    const target = e.target;

    // Validates only the given fields and returns Promise<Field[]>
    const fields = await this.form.validateFields(target);

    const fieldIsValid = fields.every(field => field.isValid());
    if (fieldIsValid) console.log(`Field '${target.name}' is valid`);
    else console.log(`Field '${target.name}' is invalid`);

    if (this.form.isValid()) console.log('The form is valid');
    else console.log('The form is invalid');
  }

  async handleSubmit(e) {
    e.preventDefault();

    // Validates the non-dirty fields and returns Promise<Field[]>
    const fields = await this.form.validateForm();

    // or simply this.form.isValid();
    const formIsValid = fields.every(field => field.isValid());

    if (formIsValid) console.log('The form is valid');
    else console.log('The form is invalid');
  }

  render() {
    return (
      <FormWithConstraints
        ref={formWithConstraints => this.form = formWithConstraints}
        onSubmit={this.handleSubmit} noValidate
      >
        <input
          name="username"
          onChange={this.handleChange}
          required minLength={3}
        />
        <FieldFeedbacks for="username">
          <FieldFeedback when="tooShort">Too short</FieldFeedback>
          <Async
            promise={checkUsernameAvailability}
            then={available => available ?
              <FieldFeedback key="1" info style={{color: 'green'}}>Username available</FieldFeedback> :
              <FieldFeedback key="2">Username already taken, choose another</FieldFeedback>
            }
          />
          <FieldFeedback when="*" />
        </FieldFeedbacks>
      </FormWithConstraints>
    );
  }
}

FieldFeedbacks
- for: string => reference to a name attribute (e.g <input name="username">), should be unique to the current form
- stop?: 'first' | 'first-error' | 'first-warning' | 'first-info' | 'no' => when to stop rendering FieldFeedbacks, by default stops at the first error encountered (FieldFeedbacks order matters)
Note: you can place FieldFeedbacks anywhere, have as many as you want for the same field, nest them, mix them with FieldFeedback... Example:
```
<input name="username" ... />

<FieldFeedbacks for="username" stop="first-warning">
  <FieldFeedbacks>
    <FieldFeedback ... />
    <Async ... />
    <FieldFeedbacks stop="first-info">
      ...
    </FieldFeedbacks>
  </FieldFeedbacks>

  <FieldFeedback ... />
  <Async ... />
</FieldFeedbacks>

<FieldFeedbacks for="username" stop="no">
  ...
</FieldFeedbacks>
```
FieldFeedback
- when?:
  - ValidityState as a string => HTML5 constraint violation name
  - '*' => matches any HTML5 constraint violation
  - 'valid' => displays the feedback only if the field is valid
  - (value: string) => boolean => custom constraint
- error?: boolean => treats the feedback as an error (default)
- warning?: boolean => treats the feedback as a warning
- info?: boolean => treats the feedback as an info
- children => what to display when the constraint matches; if missing, displays the HTML5 error message if any
Async<T> => Async version of FieldFeedback, similar API as react-promise
- promise: (value: string) => Promise<T> => a promise you want to wait for
- pending?: React.ReactNode => runs when promise is pending
- then?: (value: T) => React.ReactNode => runs when promise is resolved
- catch?: (reason: any) => React.ReactNode => runs when promise is rejected
FormWithConstraints
- validateFields(...inputsOrNames: Array<Input | string>): Promise<Field[]> => Should be called when a field changes, will re-render the proper FieldFeedbacks (and update the internal FieldsStore). Without arguments, all fields ($('[name]')) are validated.
- validateForm(): Promise<Field[]> => Should be called before to submit the form. Validates only all non-dirty fields (won't re-validate fields that have been already validated with validateFields(...)), If you want to force re-validate all fields, use validateFields() without arguments.
- isValid(): boolean => should be called after validateForm() or validateFields(), tells if the fields are valid
- hasFeedbacks(): boolean => tells if the fields have any kind of feedback
- resetFields(...inputsOrNames: Array<Input | string>): Promise<Field[]> => Resets the given fields and re-render the proper FieldFeedbacks. Without arguments, all fields ($('[name]')) are reset.
- Field =>
```
{
  name: string;
  validations: { // FieldFeedbackValidation[]
    key: number;
    type: 'error' | 'warning' | 'info' | 'whenValid';
    show: boolean | undefined;
  }[];
  isValid: () => boolean
}
```
Input
If you want to style <input>, use <Input> instead: it will add classes has-errors, has-warnings, has-infos and/or is-valid on <input> when the field is validated.
Example: <Input name="username" /> can generate <input name="username" class="has-errors has-warnings">
FYI react-form-with-constraints-bootstrap4 and react-form-with-constraints-material-ui already style the fields to match their respective frameworks.

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 (see SignUp example).

react-form-with-constraints needs a polyfill such as core-js or babel-polyfill to support IE 11 and lower. See also React JavaScript Environment Requirements.

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