How do you implement a data validation pipeline in Node.js?

Question

Accepted Answer

**Validation pipeline** — chain of validators for request data.

```javascript
class ValidationPipeline {
    constructor() {
        this.steps = [];
    }

add(validator) {
        this.steps.push(validator);
        return this;
    }

async validate(data) {
        const errors = [];
        let sanitized = { ...data };

for (const step of this.steps) {
            const result = await step(sanitized);
            if (result.errors) {
                errors.push(...result.errors);
            }
            if (result.sanitized) {
                sanitized = result.sanitized;
            }
        }

return {
            valid: errors.length === 0,
            errors,
            data: sanitized,
        };
    }
}

// Validators
const trimStrings = (data) => ({
    sanitized: Object.fromEntries(
        Object.entries(data).map(([k, v]) =>
            [k, typeof v === "string" ? v.trim() : v]
        )
    ),
});

const checkEmail = (data) => ({
    errors: data.email && !/^[^@]+@[^@]+$/.test(data.email)
        ? [{ field: "email", message: "Invalid email" }]
        : null,
});

// Pipeline
const pipeline = new ValidationPipeline()
    .add(trimStrings)
    .add(checkRequired(["name", "email"]))
    .add(checkEmail);

const result = await pipeline.validate(req.body);
if (!result.valid) return res.status(400).json({ errors: result.errors });
```

Node.js: How do you implement a data validation pipeline in Node.js?