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

joi lets you describe your data using a simple, intuitive, and readable language. Like the rest of the hapi ecosystem it fits in, joi allows you to describe your data for both input and output validation, as part of a hapi HTTP server or standalone.

See the detailed API Reference.

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

const schema = Joi.object({
    username: Joi.string()
        .alphanum()
        .min(3)
        .max(30)
        .required(),

    password: Joi.string()
        .pattern(/^[a-zA-Z0-9]{3,30}$/),

    repeat_password: Joi.ref('password'),

    access_token: [
        Joi.string(),
        Joi.number()
    ],

    birth_year: Joi.number()
        .integer()
        .min(1900)
        .max(2013),

    email: Joi.string()
        .email({ minDomainSegments: 2, tlds: { allow: ['com', 'net'] } })
})
    .with('username', 'birth_year')
    .xor('password', 'access_token')
    .with('password', 'repeat_password');


schema.validate({ username: 'abc', birth_year: 1994 });
// -> { value: { username: 'abc', birth_year: 1994 } }

schema.validate({});
// -> { value: {}, error: '"username" is required' }

// Also -

try {
    const value = await schema.validateAsync({ username: 'abc', birth_year: 1994 });
}
catch (err) { }

The above schema defines the following constraints:

• username
  • a required string
  • must contain only alphanumeric characters
  • at least 3 characters long but no more than 30
  • must be accompanied by birth_year
• password
  • an optional string
  • must satisfy the custom regex pattern
  • cannot appear together with access_token
  • must be accompanied by repeat_password and equal to it
• access_token
  • an optional, unconstrained string or number
• birth_year
  • an integer between 1900 and 2013
• email
  • a valid email address string
  • must have two domain parts e.g. example.com
  • TLD must be .com or .net

Usage is a two steps process:

First, a schema is constructed using the provided types and constraints:

const schema = Joi.object({
    a: Joi.string()
});

Note that joi schema objects are immutable which means every additional rule added (e.g. .min(5)) will return a new schema object.

Second, the value is validated against the defined schema:

const { error, value } = schema.validate({ a: 'a string' });

If the input is valid, then the error will be null. If the input is invalid, error is assigned a ValidationError object providing more information.

The schema can be a plain JavaScript object where every key is assigned a joi type, or it can be a joi type directly:

const schema = Joi.string().min(10);

If the schema is a joi type, the schema.validate(value) can be called directly on the type. When passing a non-type schema object, the module converts it internally to an object() type equivalent to:

const schema = Joi.object().keys({
    a: Joi.string()
});

When validating a schema:

• Values (or keys in case of objects) are optional by default.

  Joi.string().validate(undefined); // validates fine

  To disallow this behavior, you can either set the schema as required(), or set presence to "required" when passing options:

  Joi.string().required().validate(undefined);
  // or
  Joi.string().validate(undefined, /* options */ { presence: "required" });

• Strings are utf-8 encoded by default.

• Rules are defined in an additive fashion and evaluated in order, first the inclusive rules, then the exclusive rules.