When developing web applications, validating user input is crucial to ensure the integrity and security of your application. In the Node.js ecosystem, JOI is a powerful and flexible schema description language and data validator for JavaScript objects. It allows developers to create blueprints for JavaScript objects (an object schema) to ensure they adhere to the expected format.

In this article, we will explore the features of the JOI package and delve into its methods and functions. We will be implement a user creation Data Transfer Object (DTO) schema in a file named user.request.js for body validation middleware in an Express application.

Installation

npm i joi

Features of JOI

JOI is designed to validate JavaScript objects in a declarative way. Here are some of its notable features:

1. Schema Definition: Define the structure and rules for your data using a simple, expressive syntax.
2. Validation: Validate data against the defined schema, providing detailed error messages for invalid inputs.
3. Customization: Customize validation messages, add custom validation rules, and handle complex validation scenarios.
4. Types and Constraints: Support for various data types and constraints like strings, numbers, arrays, objects, and more.
5. Extensibility: Extend JOI's functionality with custom validators and schemas.

Key Methods and Functions

Here is a description of key methods and functions provided by JOI:

• Joi.string(): Creates a string schema.
• Joi.number(): Creates a number schema.
• Joi.object(): Creates an object schema.