express-mock-middleware

0.0.6 verified Sat Apr 25 auth: no javascript

A simple mock middleware for Express.js that allows you to define mock API responses in separate JavaScript files. Version 0.0.6 is the latest and stable release. It uses a glob pattern to load mock files (e.g., 'mock/**/*.js') where each file exports an object mapping HTTP methods and paths to handler functions. The middleware intercepts matching requests and returns mock data without requiring a real backend. It is a lightweight alternative to full mocking libraries, focusing on simplicity and ease of use. The package has minimal dependencies and is suitable for development and testing environments.

Common errors

error TypeError: mockMiddleware is not a function ↓

cause Destructuring the default export as a named import: const { mockMiddleware } = require('express-mock-middleware');

fix

Use: const mockMiddleware = require('express-mock-middleware'); or import mockMiddleware from 'express-mock-middleware';

error Cannot find module 'globby' ↓

cause Missing dependency globby is not installed automatically in some environments.

fix

Run: npm install globby --save-dev

error Mock file not loaded: no match for pattern 'mock/**/*.js' ↓

cause The glob pattern does not match any files because the cwd is incorrect or the mock directory doesn't exist.

fix

Pass cwd: __dirname in options and ensure the mock directory exists relative to that path.

error Route /api/info returned 404 ↓

cause Mock file key format is incorrect (e.g., 'GET/api/info' without space) or file not loaded.

fix

Ensure key is exactly 'GET /api/info' (space between method and path).

Warnings

gotcha Glob pattern is relative to process.cwd() by default; use cwd option to change base directory. ↓

fix Pass cwd: __dirname in options to base path on the current file.

gotcha Mock files must export an object with keys like 'METHOD /path'. Missing space causes routing failure. ↓

fix Use exact format: 'GET /api/info' or 'POST /api/submit'.

gotcha Only supports synchronous handlers; async/await or Promises not supported. ↓

fix Use callback-style middleware or provide a synchronous response.

deprecated Package has not been updated since 2015 and may contain security vulnerabilities in dependencies. ↓

fix Consider using a more actively maintained mocking library like 'express-mock-api' or 'msw'.

gotcha Middleware overwrites routes; define mock middleware before other route handlers. ↓

fix Ensure app.use(mockMiddleware(...)) is placed before app.get(...) or other routes.

Install

npm install express-mock-middleware

yarn add express-mock-middleware

pnpm add express-mock-middleware

Imports

default

wrong

const mockMiddleware = require('express-mock-middleware')

correct

import mockMiddleware from 'express-mock-middleware'

CommonJS require works as well, but ESM import is preferred for modern projects.

mockMiddleware

wrong

const { mockMiddleware } = require('express-mock-middleware')

correct

const mockMiddleware = require('express-mock-middleware')

The module exports a single function as default. Named destructuring will not work.

type

wrong

import { default as mockMiddleware } from 'express-mock-middleware'

correct

import mockMiddleware from 'express-mock-middleware'

No named export; always import default symbol.

Quickstart

Shows how to set up express-mock-middleware with a glob pattern to load mock files and start an Express server.

const express = require('express');
const mockMiddleware = require('express-mock-middleware');
const path = require('path');
const app = express();

// Define mock files in a directory, e.g., mock/
app.use(mockMiddleware({
  glob: 'mock/**/*.js', // relative to process.cwd()
  cwd: __dirname // optional, resolve from current directory
}));

app.listen(3000, () => {
  console.log('Server running on port 3000');
});

// Example mock file: mock/info.js
// module.exports = {
//   'GET /api/info': (req, res) => {
//     res.json({ success: true, data: { name: 'test' } });
//   }
// };