joilisted

# 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](reference/validation.md) 3. **Types extend base** - All types inherit from `any()`; see [types overview](reference/types.md) 4. **Refs for cross-field** - Use `Joi.ref()` for dynamic values across fields; see [references](reference/references.md) 5. **Extend for custom types** - Use `Joi.extend()` to create custom types; see [extensions](reference/extensions.md) ## Workflow 1. **Choose a type** - [types overview](reference/types.md) 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](reference/conditionals.md) 5. **Customize errors** - Override messages via `.messages()` or `.error()`; see [errors](reference/errors.md) ## Key Patterns | Topic | Reference | | ------------------------ | -------------