/ Form

Simple form validation for React

Simple form validation for React

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/

Introduction: what is HTML5 form validation?

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

input-type-email

input-required
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.

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>
  • Async validation
  • 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
  • Support for React Native with npm package react-form-with-constraints-native
  • Easily extendable
  • ...
<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>
  <FieldFeedback when={value => !/\W/.test(value)} warning>
    Should contain special characters
  </FieldFeedback>
</FieldFeedbacks>

Examples

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=*? React keys are needed otherwise it can get buggy when the user rapidly changes the input
    }
  />
</FieldFeedbacks>

Trigger validation:

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

    // 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... Dirty example:

    <div>
      <input name="username" ... />
    </div>
    
    <FieldFeedbacks for="username" stop="first-warning">
    
      <FieldFeedbacks stop="no">
        <div>
          <FieldFeedbacks stop="first-error">
            <FieldFeedbacks>
              <div><FieldFeedback ... /></div>
              <div><Async ... /></div>
              <div><FieldFeedback ... /></div>
            </FieldFeedbacks>
          </FieldFeedbacks>
        </div>
        <FieldFeedbacks>
          <FieldFeedback ... />
          <Async ... />
          <FieldFeedback ... />
    
          <FieldFeedbacks stop="first-info">
            <FieldFeedback ... />
            <Async ... />
            <FieldFeedback ... />
          </FieldFeedbacks>
    
          <FieldFeedback ... />
          <Async ... />
          <FieldFeedback ... />
        </FieldFeedbacks>
      </FieldFeedbacks>
    
      <FieldFeedbacks stop="first-info">
        <FieldFeedbacks>
          <FieldFeedback ... />
          <Async ... />
          <FieldFeedback ... />
        </FieldFeedbacks>
      </FieldFeedbacks>
    
    </FieldFeedbacks>
    
    <div>
      <FieldFeedbacks for="username" stop="no">
        ...
      </FieldFeedbacks>
    </div>
    
  • 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 known fields are valid (thanks to internal FieldsStore)

    • reset(): Promise => resets internal FieldsStore and re-render all FieldFeedbacks

    • Field =>

      {
        name: string;
        validations: {
          key: number;
          type: 'error' | 'warning' | 'info' | 'whenValid';
          show: boolean | undefined;
        }[]; // FieldFeedbackValidation[],
        isValid: () => boolean
      }
      

GitHub