Link Two Form Fields Together

You may find yourself needing to link two fields together; when one is validated as another field's value has changed. One such usage is when you have both a password and confirm_password field, where you want to confirm_password to error out when password's value does not match; regardless of which field triggered the value change.

Imagine the following userflow:

User updates confirm password field.
User updates the non-confirm password field.

In this example, the form will still have errors present, as the "confirm password" field validation has not been re-ran to mark as accepted.

To solve this, we need to make sure that the "confirm password" validation is re-run when the password field is updated. To do this, you can add a onChangeListenTo property to the confirm_password field.

tsx

function App() {
  const form = useForm({
    defaultValues: {
      password: '',
      confirm_password: '',
    },
    // ...
  })

  return (
    <div>
      <form.Field name="password">
        {(field) => (
          <label>
            <div>Password</div>
            <input
              value={field.state.value}
              onChange={(e) => field.handleChange(e.target.value)}
            />
          </label>
        )}
      </form.Field>
      <form.Field
        name="confirm_password"
        validators={{
          onChangeListenTo: ['password'],
          onChange: ({ value, fieldApi }) => {
            if (value !== fieldApi.form.getFieldValue('password')) {
              return 'Passwords do not match'
            }
            return undefined
          },
        }}
      >
        {(field) => (
          <div>
            <label>
              <div>Confirm Password</div>
              <input
                value={field.state.value}
                onChange={(e) => field.handleChange(e.target.value)}
              />
            </label>
            {field.state.meta.errors.map((err) => (
              <div key={err}>{err}</div>
            ))}
          </div>
        )}
      </form.Field>
    </div>
  )
}

function App() {
  const form = useForm({
    defaultValues: {
      password: '',
      confirm_password: '',
    },
    // ...
  })

  return (
    <div>
      <form.Field name="password">
        {(field) => (
          <label>
            <div>Password</div>
            <input
              value={field.state.value}
              onChange={(e) => field.handleChange(e.target.value)}
            />
          </label>
        )}
      </form.Field>
      <form.Field
        name="confirm_password"
        validators={{
          onChangeListenTo: ['password'],
          onChange: ({ value, fieldApi }) => {
            if (value !== fieldApi.form.getFieldValue('password')) {
              return 'Passwords do not match'
            }
            return undefined
          },
        }}
      >
        {(field) => (
          <div>
            <label>
              <div>Confirm Password</div>
              <input
                value={field.state.value}
                onChange={(e) => field.handleChange(e.target.value)}
              />
            </label>
            {field.state.meta.errors.map((err) => (
              <div key={err}>{err}</div>
            ))}
          </div>
        )}
      </form.Field>
    </div>
  )
}

This similarly works with onBlurListenTo property, which will re-run the validation when the field is blurred.