How do you implement request validation with Joi in Express?

Question

Accepted Answer

**Joi** — schema validation for request data.

```javascript
const Joi = require("joi");

// Validation schemas
const schemas = {
    createUser: Joi.object({
        name: Joi.string().min(2).max(50).required(),
        email: Joi.string().email().required(),
        password: Joi.string().min(8).pattern(/^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])/),
        age: Joi.number().integer().min(18).max(120),
    }),

updateUser: Joi.object({
        name: Joi.string().min(2).max(50),
        email: Joi.string().email(),
    }).min(1),
};

// Validation middleware
function validate(schemaName, property = "body") {
    return (req, res, next) => {
        const { error, value } = schemas[schemaName].validate(req[property], {
            abortEarly: false,
            stripUnknown: true,
        });

if (error) {
            const errors = error.details.map(d => ({
                field: d.path.join("."),
                message: d.message,
            }));
            return res.status(400).json({ errors });
        }

req[property] = value;
        next();
    };
}

// Usage
app.post("/users", validate("createUser"), (req, res) => {
    // req.body is validated and sanitized
    res.json({ data: req.body });
});

app.put("/users/:id", validate("updateUser"), (req, res) => {
    res.json({ data: req.body });
});
```

**Key points:**
- Validate all inputs (body, query, params).
- stripUnknown removes unexpected fields.
- abortEarly: false shows all errors.

Node.js: How do you implement request validation with Joi in Express?