@hapi/joi

What is @hapi/joi?

@hapi/joi is a powerful schema description language and data validator for JavaScript. It allows you to define and validate data structures in a declarative way, making it easier to ensure that your data conforms to the expected format.

What are @hapi/joi's main functionalities?

Schema Validation

This feature allows you to define a schema for your data and validate it against that schema. The example demonstrates how to create a schema for a user object and validate an instance of that object.

const Joi = require('@hapi/joi');

const schema = Joi.object({
  username: Joi.string().alphanum().min(3).max(30).required(),
  password: Joi.string().pattern(new RegExp('^[a-zA-Z0-9]{3,30}$')),
  birth_year: Joi.number().integer().min(1900).max(2013)
});

const value = {
  username: 'abc',
  password: 'password123',
  birth_year: 1990
};

const result = schema.validate(value);
console.log(result);

Custom Error Messages

This feature allows you to customize error messages for different validation rules. The example shows how to provide custom error messages for the username and password fields.

const Joi = require('@hapi/joi');

const schema = Joi.object({
  username: Joi.string().alphanum().min(3).max(30).required().messages({
    'string.base': 'Username should be a type of text',
    'string.empty': 'Username cannot be an empty field',
    'string.min': 'Username should have a minimum length of {#limit}',
    'any.required': 'Username is a required field'
  }),
  password: Joi.string().pattern(new RegExp('^[a-zA-Z0-9]{3,30}$')).messages({
    'string.pattern.base': 'Password must be alphanumeric and between 3 to 30 characters'
  })
});

const value = {
  username: '',
  password: 'pw'
};

const result = schema.validate(value);
console.log(result.error.details);

Async Validation

This feature allows you to perform asynchronous validation, such as checking if an email is already taken in a database. The example demonstrates how to use an external async validation function within a Joi schema.

const Joi = require('@hapi/joi');

const schema = Joi.object({
  email: Joi.string().email().external(async (value, helpers) => {
    const isEmailTaken = await checkEmailInDatabase(value); // hypothetical async function
    if (isEmailTaken) {
      throw new Error('Email is already taken');
    }
    return value;
  })
});

async function validateEmail(email) {
  try {
    await schema.validateAsync({ email });
    console.log('Email is valid');
  } catch (err) {
    console.error(err.message);
  }
}

validateEmail('[e-mail]');

Other packages similar to @hapi/joi

yup

Yup is a JavaScript schema builder for value parsing and validation. It is similar to @hapi/joi in that it allows you to define schemas and validate data against them. However, Yup is often considered to be more lightweight and has a more modern API.

validator

Validator is a library of string validators and sanitizers. Unlike @hapi/joi, which is a comprehensive schema validation library, Validator focuses on providing a wide range of functions for validating and sanitizing strings.

ajv

Ajv is a JSON schema validator that is highly performant and supports JSON Schema standards. It is different from @hapi/joi in that it uses JSON Schema for validation, making it a good choice for applications that need to adhere to JSON Schema standards.

README

@hapi/joi

The most powerful schema description language and data validator for JavaScript.

joi is part of the hapi ecosystem and was designed to work seamlessly with the hapi web framework and its other components (but works great on its own or with other frameworks). If you are using a different web framework and find this module useful, check out hapi – they work even better together.

Visit the hapi.dev Developer Portal for tutorials, documentation, and support

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