'TypeError: validator is not a function' after installing and requiring express-validator

Question

I have installed express validator with npm install express-validator --save and required it in my app.js. However when I ran npm start the terminal says it's not a function.

In my app.js:

var validator = require("express-validator");
app.use(validator());

In my package.json dependencies:

"express-validator": "^6.0.1"

Response from terminal:

app.use(validator());
        ^

TypeError: validator is not a function
    at Object.<anonymous> (/mnt/e/CODING/Templates/leaftunehoney/SC2/app.js:30:9)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Module.require (module.js:596:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/mnt/e/CODING/Templates/leaftunehoney/SC2/bin/www:7:11)`    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Function.Module.runMain (module.js:693:10)
    at startup (bootstrap_node.js:188:16)

What's causing the problem?

Answer 1

Maintainer here.
You seem to be using the latest version. express-validator v6 has been released a few days ago, and it no longer includes what was called the "legacy API".

You should migrate to the new APIs (what previously was under express-validator/check, for example); the getting started guide* should give you enough information to help with it.

E.g.

const { check, validationResult } = require('express-validator');

app.post('/user', [
  check('username').isEmail(),
  check('password').isLength({ min: 5 })
], (req, res) => {
  const errors = validationResult(req);
  if (!errors.isEmpty()) {
    return res.status(422).json({ errors: errors.array() });
  }

  // create/update the user however you want?
});

_{* There are no official migration guides as of now because the new API has been around for a few years.}