How do I Solve Express Validator Middleware Error?

First, I have userController like this:

File userController.js

const { validationResults } = require('express-validator');
const { userSignUpValidation } = require('../validator/userSignUpValidate');


function userCreation(req, res) {
    try{
        const errors = validationResults(req);
        if(errors) {
            return res.status(400)
            .json({
                error: {
                    message: errors.array()[0].msg
                }
            })
        }

        bcrypt.hash(req.body.userPassword, saltRounds, function(err, hash) {
            User.create({
                userId: req.body.userId,
                userEmail: req.body.userEmail,
                userPhoneNumber: req.body.userPhoneNumber,
                userPassword: hash
            })
            .then((user) => {
                return res.status(200).json(user);
            })
            .catch((error) => {
                return res.status(400).json.error;
            });
        });
    } catch(error) {
        return res.status(400)
        .json({
            error: {
                message: error
            }
        })
    }
}

In the validator/userSignUpValidate.js the code like this:

'use strict'

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

module.exports = [
    check('userId').isLength({ min: 5 }).withMessage('The username at least more than 5 characters!'),
    check('userPassword').isLength({ min: 6 }).withMessage('The password at least more than 6 characters!'),
    check('userPhoneNumber').isLength({ min: 10 }).withMessage('The phone number at least more than 10 characters!'),
    check('userEmail').isEmail().withMessage('Is your email correct? Please be correct!')
]

When I test it on postman, the json response always show error by catch on userController.js without error message.

{
    "error": {
        "message": {}
    }
}

<br>
My question. To ensure the express-validator run in the right place, where should I put the code?

Firstly you need to import validationResult from express-validator, in your code you are importing validationResults.

Secondly, you are not using your userSignUpValidate middleware. This middleware can be used in controller but it is better to appy it in the userRoute to keep controller clean.

So let's apply userSignUpValidate middleware to the userRoutes.
If the file paths don't match yours, please fix them.

const express = require("express");
const router = express.Router();
const usersController = require("../controllers/userController");
const userSignUpValidate = require("../validator/userSignUpValidate");

router.post("/register", [userSignUpValidate], usersController.userCreation);

module.exports = router;

Then in the controller, we need to import validationResult from express-validator and use it:

const { validationResult } = require("express-validator");

function userCreation(req, res) {
  try {
    const errors = validationResult(req);
    if(!errors.isEmpty()) {
      console.log(errors);
      return res.status(400).json({
        error: {
          message: errors.array()[0].msg
        }
      });
    }

    //other code you have
  } catch (error) {
    return res.status(400).json({
      error: {
        message: error
      }
    });
  }
}

exports.userCreation = userCreation;

When we send a request body with a 3 character password like this:

{
  "userId": "userid",
  "userPassword": "123",
  "userPhoneNumber": "1234567890",
  "userEmail": "abc@gmail.com"
}

The response will be like this with a 400 - Bad Request:

{
    "error": {
        "message": "The password at least more than 6 characters!"
    }
}

you should pass like this

const errors = validationResults(req.body);

 const Joi = require('@hapi/joi');                                           
 const loginValidation = data =>{    const schema = {
    username: Joi.string().min(5).required(),
    password: Joi.string().min(5).required(),
    deviceId: Joi.string().min(2).required()
};
return Joi.validate(data, schema); };                   
module.exports.loginValidation = loginValidation;                                 

> My Routes File

const { registerValidation, loginValidation } = require('../../validation');   router.post('/login', async (req, res)=>{
try {
    //validate the data to be submitted
    const { error } = loginValidation(req.body);
    if (error) return res.status(200).send(
        {
            status: 0,
            message: "Validarion Error",
            details: error.details[0].message
        });
         
} catch (error) {
    res.status(400).send({
        status: 0,
        message: "Failed",
        error: error
    });
}});

this code works fine and is in production mode

Just try like below,

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


const app = express();

//this function you need to export in controller
const xxx = (req, res, next) => {
  try {
    validationResult(req).throw();
    res.status(200).send('success');
  } catch (err) {
    console.log('error messagecame')
    res.status(422).json(err);
  }
}

app.get('/', oneOf([
  check('lang').isIn(['js', 'react', 'angular'])
]), xxx);

app.listen(4000, ()=>{
  console.log("running server 4k")
})

Sample working copy

UPDATE 2

I hope below one will help full,

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

const app = express();
const xxx = [
  check('lang').isIn(['js', 'react', 'angular']),
  (req, res, next) => {
    try {
      validationResult(req).throw();
      res.status(200).send('success');
    } catch (err) {
      console.log('error messagecame')
      res.status(422).json(err);
    }
  }
]

app.get('/', xxx);

app.listen(4000, ()=>{
  console.log("running server 4k")
})

SAMPLE WORKING COPY2

Error

https://TruthfulWeirdIrc--five-nine.repl.co?lang=jssddf

Success

https://TruthfulWeirdIrc--five-nine.repl.co?lang=js