Validate One Field or Step

Running every rule after each keystroke wastes work and can show errors for fields the user has not touched. With Vest, the UI says what changed and the suite keeps the other results.

const result = signupSuite.only('email').run(formData);

Only tests named email execute. Passing or failing results for fields such as username and password remain available.

The result still contains the other fields

const data = {
  bio: 'TypeScript developer',
  password: 'short',
  username: 'al',
};

let result = profileSuite.only('username').run(data);
result.hasErrors('username'); // true
result.isTested('password'); // false

result = profileSuite.only('password').run(data);
result.hasErrors('password'); // true
result.hasErrors('username'); // still true

data.username = 'alice';
result = profileSuite.only('username').run(data);
result.isValid('username'); // true
result.hasErrors('password'); // still true

The second run does not replace the result with a password-only object. Vest reconciles the new password tests with the username result already stored by the suite.

function validateField(field, nextValues) {
  const result = signupSuite.only(field).run(nextValues);

  return {
    errors: result.getErrors(field),
    pending: result.isPending(field),
    tested: result.isTested(field),
  };
}

For several fields or a workflow step, use focus:

signupSuite.focus({ only: ['country', 'city', 'postalCode'] }).run(formData);

signupSuite.focus({ onlyGroup: 'shipping' }).run(formData);

Focus belongs at the interaction call site because the UI knows what changed. Business-driven inclusion—such as a dependent field—belongs inside the suite.

Full validation still matters

Before progressing through a guarded step, run the step group and await it. Before final submission, run the whole suite:

const step = await signupSuite.focus({ onlyGroup: 'shipping' }).run(formData);

if (step.isValidByGroup('shipping')) {
  goToNextStep();
}

const complete = await signupSuite.run(formData);

Focused validation changes what runs now. It does not redefine the complete validity requirements.

Common mistakes

Mistake	Correction
Passing only the focused field when rules read other values	Pass the current complete form object
Using focus({ omit: field })	The call-site modifier is skip; omitWhen has different suite semantics
Checking global isValid() before required fields have run	Use field or group selectors during progression and run the full suite on submit
Putting UI event focus inside the suite callback	Let the interaction choose suite.only() or suite.focus()

Try adding a display name that depends on username, then focus both fields when either value changes.

Read the focus modifier reference.