express-init

1.1.2 verified Sat Apr 25 auth: no javascript maintenance

Express middleware initialization utility that allows middleware to perform asynchronous setup before the server starts. Version 1.1.2 supports Express 4.x. It calls a user-defined `init` function on each middleware serially before invoking a final callback. Unlike other async setup patterns (e.g., Promises), it uses callbacks and is tightly coupled to Express middleware structure. Maintenance is low; last release was several years ago. Differentiating factor: lightweight, no additional dependencies, and middleware-based initialization pattern.

Common errors

error initialize is not a function ↓

cause Using ES module import syntax on a CJS-only module.

fix

Use const initialize = require('express-init'); instead of import initialize from 'express-init';

error TypeError: middleware.init is not a function ↓

cause Middleware attached to app does not have an `init` function defined.

fix

Add an init function to your middleware: middleware.init = function(app, callback) { ... }

error Callback must be a function ↓

cause The second argument to initialize() is missing or not a function.

fix

Call initialize(app, function(err) { ... }) with a valid callback.

Warnings

breaking Only supports Express 4.x. Not compatible with Express 3.x or 5.x. ↓

fix Ensure your Express version is 4.x.

deprecated The package uses callback-based asynchronous pattern. Modern codebases prefer Promises or async/await. ↓

fix Consider wrapping initialization in a Promise or using alternative libraries that support async/await.

gotcha Middleware init functions are called only once, even if the middleware is used multiple times in the same app. ↓

fix Ensure that your init function does not rely on being called multiple times.

gotcha The library does not handle errors from init functions gracefully; throwing in init will crash the process. ↓

fix Always call callback with an error if initialization fails; do not throw.

gotcha Works only with middleware that have an `init` function attached. Middleware without init are skipped silently. ↓

fix Ensure your middleware explicitly defines an `init` method if async initialization is needed.

Install

npm install express-init

yarn add express-init

pnpm add express-init

Imports

default
wrong
```
import initialize from 'express-init';
```
correct
```
const initialize = require('express-init');
```
This package is CJS-only and does not support ES modules. Use require() only.
default (TypeScript)
wrong
```
import initialize from 'express-init';
```
correct
```
import initialize = require('express-init');
```
In TypeScript with CJS modules, use `import = require()` syntax.
initialize
wrong
```
var init = require('express-init').init;
```
correct
```
const init = require('express-init');
init(app, callback);
```
The module exports a single function directly; do not destructure or access .init property.

Quickstart

Demonstrates defining an Express middleware with an init function and using express-init to initialize all middleware before starting the server.

const express = require('express');
const initialize = require('express-init');

const app = express();

const myMiddleware = (req, res, next) => {
  console.log('Request received');
  next();
};
myMiddleware.init = (app, callback) => {
  // Simulate async init (e.g., DB connection)
  setTimeout(() => {
    console.log('Middleware initialized');
    callback();
  }, 100);
};

app.use(myMiddleware);
app.get('/', (req, res) => res.send('Hello'));

initialize(app, (err) => {
  if (err) throw err;
  app.listen(3000, () => console.log('Server started'));
});