Joi

Quick Start

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

const schema = Joi.object({
    name: Joi.string().min(1).max(100).required(),
    age: Joi.number().integer().min(0),
    email: Joi.string().email()
});

const { error, value } = schema.validate(input);

Critical Rules

1. Schemas are immutable - Every method returns a new schema instance; never mutate
2. Validate at boundaries - Use

   validate()

   or

   attempt()

   at input boundaries; see validation
3. Types extend base - All types inherit from

   any()

   ; see types overview
4. Refs for cross-field - Use

   Joi.ref()

   for dynamic values across fields; see references
5. Extend for custom types - Use

   Joi.extend()

   to create custom types; see extensions

Workflow

1. Choose a type - types overview for all built-in types
2. Add constraints - Chain rules like

   .min()

   ,

   .max()

   ,

   .pattern()

   ,

   .valid()

3. Compose schemas - Nest

   Joi.object()

   ,

   Joi.array()

   ,

   Joi.alternatives()

4. Add conditionals - Use

   .when()

   for dynamic schemas; see conditionals
5. Customize errors - Override messages via

   .messages()

   or

   .error()

   ; see errors

Key Patterns