api-validation-error-handler

A clean reusable Express middleware for handling validation errors produced by express-validator, providing unified API responses and localization support. This middleware reduces repeated error handling logic and keeps controllers clean.

📦 Installation

npm install api-validation-error-handler

or

yarn add api-validation-error-handler

✨ Features

✔ Handles validation errors automatically ✔ Converts errors into key/value structure ✔ Uses standard API response format via express-api-responses ✔ Keeps controllers clean and focused

🚀 Usage

1. Import middleware

import { handleValidationErrors } from "api-validation-error-handler";

or using CommonJS:

const { handleValidationErrors } = require("api-validation-error-handler");

2. Apply validator and middleware

import express from "express";
import { body } from "express-validator";
import { handleValidationErrors } from "api-validation-error-handler";

const router = express.Router();

router.post(
  "/books",
  [
    body("name")
      .notEmpty()
      .withMessage((value, { req }) => "Name is required"),
    body("price")
      .isFloat({ gt: 0 })
      .withMessage((value, { req }) => "Price must be greater than 0"),
  ],
  handleValidationErrors(), // 🚨 always after validators
  (req, res) => {
    res.json({ status: true, message: "Book created successfully" });
  }
);

export default router;

🎛 Custom Message Key

You can override the returned message:

handleValidationErrors("Input validation error")

Example:

router.post(
  "/login",
  [
    body("email")
      .isEmail()
      .withMessage((v, { req }) => "Invalid email format"),
  ],
  handleValidationErrors("Login validation failed"),
  loginController
);

📤 Response Format

If validation fails:

{
    "statusCode": 400,
    "status": false,
    "message": "failed to login",
    "data": null,
    "errors": {
        "email": "email address is invalid"
    }
}

If validation succeeds:

➡ Controller continues normally.

🧠 How It Works

It checks validation errors, formats them, and returns an API response:

• Key = field name
• Value = validation message

Example formatted output:

{
  "name": "Name is required",
  "price": "Price must be greater than 0"
}

📌 Notes & Recommendations

• Put this middleware after validation rules

• Works with:

  • body()
  • param()
  • query()

• Keeps response structure consistent across the API

🧑‍💻 Requirements

This package depends on:

• express-validator
• express-api-responses

Ensure they are installed in your project.

🏁 Summary

Use handleValidationErrors() in any route to avoid manually checking validation results and formatting error responses. This middleware is ideal for large-scale Express REST APIs where consistent error handling is required.

📌 For suggestions, improvements, or feature requests—open an issue anytime.