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Validation with Zod in Node.js

Validation is critical for ensuring that the data entering your application meets your expectations. Zod is a TypeScript-first schema declaration and validation library.

Why Zod?

  • Zero dependencies: Extremely lightweight.
  • TypeScript first: Automatically infers types from your schemas.
  • Concise API: Easy to read and write.
  • Works with JS: Full support for JavaScript environments.

Installation

Terminal window
npm install zod

Basic Usage

const { z } = require('zod');


// Define a schema
const UserSchema = z.object({
  username: z.string().min(3),
  email: z.string().email(),
  age: z.number().optional(),
});


// Parse data
try {
  const result = UserSchema.parse({
    username: 'johndoe',
    email: 'john@example.com',
  });
  console.log('Valid data:', result);
} catch (e) {
  console.error('Validation failed:', e.errors);
}

Using with Express Middleware

Zod is excellent for validating request bodies, query parameters, and headers.

const validate = (schema) => (req, res, next) => {
  try {
    schema.parse(req.body);
    next();
  } catch (e) {
    return res.status(400).json(e.errors);
  }
};


app.post('/user', validate(UserSchema), (req, res) => {
  res.send('User created');
});

Features

  • Transformations: Transform data while validating (e.g., trim strings).
  • Default values: Provide defaults if a field is missing.
  • Custom Validations: Implement complex logic with refine().
  • Error Messages: Customize error messages for better user experience.