yup

Yup

Schema validation library with a fluent, chainable API for JavaScript and TypeScript.

Quick Start

npm install yup

import * as yup from 'yup';

const schema = yup.object({
  name: yup.string().required(),
  email: yup.string().email().required(),
  age: yup.number().positive().integer(),
});

// Validate
const data = await schema.validate({ name: 'John', email: 'john@example.com' });

// Check validity
const isValid = await schema.isValid(data);

Schema Types

String

yup.string()
  .required('Name is required')
  .min(2, 'At least 2 characters')
  .max(50, 'At most 50 characters')
  .matches(/^[a-zA-Z]+$/, 'Only letters')
  .email('Invalid email')
  .url('Invalid URL')
  .uuid('Invalid UUID')
  .lowercase()
  .uppercase()
  .trim()
  .default('Anonymous')

Number

yup.number()
  .required('Required')
  .min(0, 'Must be positive')
  .max(100, 'Max 100')
  .positive('Must be positive')
  .negative('Must be negative')
  .integer('Must be integer')
  .moreThan(0, 'Greater than 0')
  .lessThan(100, 'Less than 100')
  .truncate()
  .round()
  .default(0)

Boolean

yup.boolean()
  .required()
  .isTrue('Must accept terms')
  .isFalse()
  .default(false)

Date

yup.date()
  .required()
  .min(new Date(), 'Must be in the future')
  .max(new Date('2030-12-31'), 'Too far ahead')
  .default(() => new Date())

Array

yup.array()
  .of(yup.string().required())
  .min(1, 'At least one item')
  .max(5, 'At most 5 items')
  .required()
  .default([])

// Tuple-like array
yup.tuple([
  yup.string().required(),
  yup.number().required(),
])

Object

yup.object({
  name: yup.string().required(),
  age: yup.number().positive(),
})
  .noUnknown() // Reject unknown keys
  .strict()    // Don't coerce types

Mixed (Any Type)

yup.mixed()
  .oneOf(['option1', 'option2'], 'Must be option1 or option2')
  .notOneOf(['forbidden'])
  .required()

Common Patterns

User Registration

const registrationSchema = yup.object({
  email: yup.string()
    .email('Invalid email')
    .required('Email is required'),

  password: yup.string()
    .min(8, 'At least 8 characters')
    .matches(/[a-z]/, 'Need lowercase letter')
    .matches(/[A-Z]/, 'Need uppercase letter')
    .matches(/[0-9]/, 'Need number')
    .required('Password is required'),

  confirmPassword: yup.string()
    .oneOf([yup.ref('password')], 'Passwords must match')
    .required('Confirm password'),

  age: yup.number()
    .positive()
    .integer()
    .min(18, 'Must be 18+')
    .required('Age is required'),

  terms: yup.boolean()
    .isTrue('Must accept terms'),
});

Address

const addressSchema = yup.object({
  street: yup.string().required(),
  city: yup.string().required(),
  state: yup.string().length(2).required(),
  zip: yup.string()
    .matches(/^\d{5}(-\d{4})?$/, 'Invalid ZIP')
    .required(),
  country: yup.string().default('US'),
});

Payment

const paymentSchema = yup.object({
  cardNumber: yup.string()
    .matches(/^\d{16}$/, 'Invalid card number')
    .required(),

  expiry: yup.string()
    .matches(/^(0[1-9]|1[0-2])\/\d{2}$/, 'MM/YY format')
    .required(),

  cvv: yup.string()
    .matches(/^\d{3,4}$/, 'Invalid CVV')
    .required(),

  amount: yup.number()
    .positive()
    .required(),
});

Conditional Validation

when() - Field Dependencies

const schema = yup.object({
  hasCompany: yup.boolean(),

  companyName: yup.string().when('hasCompany', {
    is: true,
    then: (schema) => schema.required('Company name required'),
    otherwise: (schema) => schema.notRequired(),
  }),
});

Multiple Conditions

const schema = yup.object({
  type: yup.string().oneOf(['personal', 'business']),
  taxId: yup.string(),
  ssn: yup.string(),
}).test('tax-info', 'Tax info required', function(value) {
  if (value.type === 'business') {
    return !!value.taxId;
  }
  return !!value.ssn;
});

Custom Validation

test() Method

const schema = yup.string().test(
  'is-valid-username',
  'Username already taken',
  async (value) => {
    if (!value) return true;
    const available = await checkUsername(value);
    return available;
  }
);

With Context

const schema = yup.object({
  password: yup.string().required(),
  confirmPassword: yup.string()
    .test('passwords-match', 'Passwords must match', function(value) {
      return value === this.parent.password;
    }),
});

addMethod() - Reusable Validators

yup.addMethod(yup.string, 'phone', function(message) {
  return this.test('phone', message || 'Invalid phone', (value) => {
    if (!value) return true;
    return /^\+?[\d\s-()]+$/.test(value);
  });
});

// Usage
const schema = yup.object({
  phone: yup.string().phone('Invalid phone number'),
});

Type Inference

InferType

const userSchema = yup.object({
  name: yup.string().required(),
  email: yup.string().email().required(),
  age: yup.number().positive(),
});

type User = yup.InferType<typeof userSchema>;
// { name: string; email: string; age: number | undefined }

With Defaults

const schema = yup.object({
  role: yup.string().default('user'),
  active: yup.boolean().default(true),
});

type Config = yup.InferType<typeof schema>;
// { role: string; active: boolean }

Transformation

cast() - Transform Values

const schema = yup.string().trim().lowercase();
const result = schema.cast('  HELLO  '); // 'hello'

transform() - Custom Transforms

const schema = yup.string().transform((value) => {
  return value?.replace(/\s+/g, ' ').trim();
});

Object Transform

const schema = yup.object({
  firstName: yup.string(),
  lastName: yup.string(),
}).transform((value) => ({
  ...value,
  fullName: `${value.firstName} ${value.lastName}`,
}));

Validation Options

validate()

try {
  const result = await schema.validate(data, {
    abortEarly: false,      // Collect all errors
    stripUnknown: true,     // Remove unknown keys
    strict: false,          // Allow coercion
    context: { user: currentUser },
  });
} catch (err) {
  if (err instanceof yup.ValidationError) {
    console.log(err.errors);  // All error messages
    console.log(err.inner);   // Detailed errors
  }
}

validateSync()

try {
  const result = schema.validateSync(data);
} catch (err) {
  // Handle error
}

isValid()

const valid = await schema.isValid(data);

React Hook Form Integration

import { useForm } from 'react-hook-form';
import { yupResolver } from '@hookform/resolvers/yup';

const schema = yup.object({
  email: yup.string().email().required(),
  password: yup.string().min(8).required(),
});

type FormData = yup.InferType<typeof schema>;

function Form() {
  const { register, handleSubmit, formState: { errors } } = useForm<FormData>({
    resolver: yupResolver(schema),
  });

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <input {...register('email')} />
      {errors.email && <span>{errors.email.message}</span>}

      <input {...register('password')} type="password" />
      {errors.password && <span>{errors.password.message}</span>}

      <button type="submit">Submit</button>
    </form>
  );
}

Formik Integration

import { Formik, Form, Field, ErrorMessage } from 'formik';

const schema = yup.object({
  email: yup.string().email().required(),
});

function MyForm() {
  return (
    <Formik
      initialValues={{ email: '' }}
      validationSchema={schema}
      onSubmit={handleSubmit}
    >
      <Form>
        <Field name="email" type="email" />
        <ErrorMessage name="email" />
        <button type="submit">Submit</button>
      </Form>
    </Formik>
  );
}

See references/methods.md for complete method reference.