Getting Started

express-validator is a set of express.js middlewares that wraps validator.js validator and sanitizer functions.

Installation

Install it using npm (make sure that you have Node.js 8 or newer):

npm install --save express-validator

Basic guide

It's recommended that you have basic knowledge of the express.js module before you go on with this guide.

Let's get started by writing a basic route to create a user in the database:

JavaScript

const express = require('express');
const app = express();

app.use(express.json());
app.post('/user', (req, res) => {
  User.create({
    username: req.body.username,
    password: req.body.password,
  }).then(user => res.json(user));
});

TypeScript

import express from 'express';
const app = express();

app.use(express.json());
app.post('/user', (req: express.Request, res: express.Response) => {
  User.create({
    username: req.body.username,
    password: req.body.password,
  }).then(user => res.json(user));
});

Then, you'll want to make sure that you validate the input and report any errors before creating the user:

JavaScript

// ...rest of the initial code omitted for simplicity.
const { body, validationResult } = require('express-validator');

app.post(
  '/user',
  // username must be an email
  body('username').isEmail(),
  // password must be at least 5 chars long
  body('password').isLength({ min: 5 }),
  (req, res) => {
    // Finds the validation errors in this request and wraps them in an object with handy functions
    const errors = validationResult(req);
    if (!errors.isEmpty()) {
      return res.status(400).json({ errors: errors.array() });
    }

    User.create({
      username: req.body.username,
      password: req.body.password,
    }).then(user => res.json(user));
  },
);

TypeScript

// ...rest of the initial code omitted for simplicity.
import { body, validationResult } from 'express-validator';

app.post(
  '/user',
  // username must be an email
  body('username').isEmail(),
  // password must be at least 5 chars long
  body('password').isLength({ min: 5 }),
  (req: express.Request, res: express.Response) => {
    // Finds the validation errors in this request and wraps them in an object with handy functions
    const errors = validationResult(req);
    if (!errors.isEmpty()) {
      return res.status(400).json({ errors: errors.array() });
    }

    User.create({
      username: req.body.username,
      password: req.body.password,
    }).then(user => res.json(user));
  },
);

Voila! Now, whenever a request that includes invalid username or password fields is submitted, your server will respond like this:

{
  "errors": [
    {
      "location": "body",
      "msg": "Invalid value",
      "param": "username"
    }
  ]
}

For all the available validators in express-validator (just like its options), take a look at validator.js docs here.

What's next

This completes the basic guide on getting started with express-validator.
You might want to continue reading about some of the more advanced features available:

• Sanitization
• Custom validators/sanitizers
• Custom error messages
• Wildcards
• Schema validation