Conditional Validation in Yup

Question

I have an email field that only gets shown if a checkbox is selected (boolean value is true). When the form get submitted, I only what this field to be required if the checkbox is checked (boolean is true).

This is what I've tried so far:

    const validationSchema = yup.object().shape({
       email: yup
             .string()
             .email()
             .label('Email')
             .when('showEmail', {
                 is: true,
                 then: yup.string().required('Must enter email address'),
             }),
        })

I've tried several other variations, but I get errors from Formik and Yup:

Uncaught (in promise) TypeError: Cannot read property 'length' of undefined at yupToFormErrors (formik.es6.js:6198) at formik.es6.js:5933 at <anonymous> yupToFormErrors @ formik.es6.js:6198

And I get validation errors from Yup as well. What am I doing wrong?

Answer 1

You probably aren't defining a validation rule for the showEmail field.

I've done a CodeSandox to test it out and as soon as I added:

showEmail: yup.boolean()

The form started validation correctly and no error was thrown.

This is the url: https://codesandbox.io/s/74z4px0k8q

And for future this was the correct validation schema:

validationSchema={yup.object().shape({
    showEmail: yup.boolean(),
    email: yup
      .string()
      .email()
      .when("showEmail", {
        is: true,
        then: yup.string().required("Must enter email address")
      })
  })
}

Answer 2

Totally agree with @João Cunha's answer. Just a supplement for the use case of Radio button.

When we use radio button as condition, we can check value of string instead of boolean. e.g. is: 'Phone'

const ValidationSchema = Yup.object().shape({
  // This is the radio button.
  preferredContact: Yup.string()
    .required('Preferred contact is required.'),
  // This is the input field.
  contactPhone: Yup.string()
    .when('preferredContact', {
      is: 'Phone',
      then: Yup.string()
        .required('Phone number is required.'),
    }),
  // This is another input field.
  contactEmail: Yup.string()
    .when('preferredContact', {
      is: 'Email',
      then: Yup.string()
        .email('Please use a valid email address.')
        .required('Email address is required.'),
    }),

});

This the radio button written in ReactJS, onChange method is the key to trigger the condition checking.

<label>
  <input
    name="preferredContact" type="radio" value="Email"
    checked={this.state.preferredContact == 'Email'}
    onChange={() => this.handleRadioButtonChange('Email', setFieldValue)}
  />
  Email
</label>
<label>
  <input
    name="preferredContact" type="radio" value="Phone"
    checked={this.state.preferredContact == 'Phone'}
    onChange={() => this.handleRadioButtonChange('Phone', setFieldValue)}
  />
  Phone
</label>

And here's the callback function when radio button get changed. if we are using Formik, setFieldValue is the way to go.

handleRadioButtonChange(value, setFieldValue) {
  this.setState({'preferredContact': value});
  setFieldValue('preferredContact', value);
}