javascript 35 lines · 8 steps

A reusable validation middleware in Express

Turn an express-validator rule schema into a single middleware that validates, formats errors, and exposes clean data.

Explained by highlit

Express Intermediate middleware validation higher-order-functions input-sanitization error-handling

1const { validationResult, matchedData } = require('express-validator');
2 
3function validate(schema) {
4  const runners = schema.map((rule) => rule.run.bind(rule));
5 
6  return async (req, res, next) => {
7    await Promise.all(runners.map((run) => run(req)));
8 
9    const result = validationResult(req);
10    if (!result.isEmpty()) {
11      return res.status(422).json({
12        error: 'ValidationError',
13        details: result.array().map(({ path, msg, value }) => ({
14          field: path,
15          message: msg,
16          value,
17        })),
18      });
19    }
20 
21    req.validated = matchedData(req, { includeOptionals: false });
22    return next();
23  };
24}
25 
26const { body } = require('express-validator');
27 
28const createUserRules = [
29  body('email').trim().isEmail().withMessage('must be a valid email').normalizeEmail(),
30  body('password').isLength({ min: 8 }).withMessage('must be at least 8 characters'),
31  body('displayName').optional().trim().isLength({ max: 60 }).escape(),
32  body('age').optional().isInt({ min: 13, max: 120 }).toInt(),
33];
34 
35module.exports = { validate, createUserRules };

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STEP 01

Walkthrough

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Three takeaways

1A middleware factory lets you configure behavior once and reuse it across many routes.
2Running all validators with Promise.all validates fields concurrently before checking results.
3matchedData gives you only the validated, sanitized fields, keeping raw input out of your handlers.

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