feat: add native .env file loading support

examples/env-variables/.env

@@ -0,0 +1,12 @@
+# Application Configuration
+APP_NAME=Express Env Example
+APP_ENV=development
+
+# Server Configuration
+PORT=5000
+DEBUG=true
+
+# API Configuration
+API_URL=https://api.example.com
+MAX_ITEMS=100
+

examples/env-variables/index.js

@@ -0,0 +1,105 @@
+'use strict'
+
+/**
+ * Module dependencies.
+ */
+
+var express = require('../../');
+
+// Automatically loads .env, .env.[NODE_ENV], and .env.local
+
+// Option 1: Simple load
+express.loadEnv();
+
+// Option 2: Load with file watching
+// Uncomment below to enable automatic reloading when .env files change
+/*
+ const unwatch = express.loadEnv({
+  watch: true,
+  onChange: (changed, loaded) => {
+    console.log('Environment variables changed:', changed);
+  },
+  onError: (err) => {
+    console.error('Error reloading .env:', err.message);
+  }
+});
+
+// Cleanup on shutdown
+process.on('SIGINT', () => {
+  unwatch();
+  process.exit();
+});
+
+*/
+
+var app = module.exports = express();
+var logger = require('morgan');
+
+// custom log format
+if (process.env.NODE_ENV !== 'test') app.use(logger(':method :url'))
+
+app.get('/', function(req, res){
+  var nodeEnv = process.env.NODE_ENV || 'development';
+  res.send('<h1>Environment Variables Example</h1>'
+    + '<p>This example demonstrates how to use Express built-in .env file loading.</p>'
+    + '<p><strong>Current Environment:</strong> ' + nodeEnv + '</p>'
+    + '<ul>'
+    + '<li><a href="/env">View loaded environment variables</a></li>'
+    + '<li><a href="/config">View application configuration</a></li>'
+    + '</ul>'
+    + '<hr>'
+    + '<p><strong>Features:</strong></p>'
+    + '<ul>'
+    + '<li>Automatically loads .env, .env.[NODE_ENV], and .env.local files</li>'
+    + '<li>Optional file watching for automatic reloads (see source code)</li>'
+    + '<li>Environment-specific configuration</li>'
+    + '<li>Cascading values with .env.local overrides</li>'
+    + '</ul>'
+    + '<hr>'
+    + '<p><strong>Try running with different environments:</strong></p>'
+    + '<pre>NODE_ENV=development node index.js\nNODE_ENV=production node index.js</pre>'
+    + '<p><strong>Enable watch mode:</strong> Uncomment the watch example in index.js and modify your .env file to see live updates!</p>');
+});
+
+app.get('/env', function(req, res){
+  // Display some environment variables
+  var safeEnvVars = {
+    APP_NAME: process.env.APP_NAME,
+    APP_ENV: process.env.APP_ENV,
+    PORT: process.env.PORT,
+    DEBUG: process.env.DEBUG,
+    API_URL: process.env.API_URL,
+    MAX_ITEMS: process.env.MAX_ITEMS
+  };
+
+  res.send('<h1>Environment Variables</h1>'
+    + '<p>The following variables were loaded from .env file:</p>'
+    + '<pre>' + JSON.stringify(safeEnvVars, null, 2) + '</pre>'
+    + '<p><a href="/">Back to home</a></p>');
+});
+
+app.get('/config', function(req, res){
+  // Use environment variables for configuration
+  var config = {
+    appName: process.env.APP_NAME,
+    environment: process.env.APP_ENV,
+    port: process.env.PORT || 3000,
+    debug: process.env.DEBUG === 'true',
+    apiUrl: process.env.API_URL,
+    maxItems: parseInt(process.env.MAX_ITEMS) || 10
+  };
+
+  res.send('<h1>Application Configuration</h1>'
+    + '<p>Configuration built from environment variables:</p>'
+    + '<pre>' + JSON.stringify(config, null, 2) + '</pre>'
+    + '<p><a href="/">Back to home</a></p>');
+});
+
+/* istanbul ignore next */
+if (!module.parent) {
+  var port = process.env.PORT || 3000;
+  app.listen(port);
+  console.log('Express started on port ' + port);
+  console.log('App Name: ' + (process.env.APP_NAME || 'Not set'));
+  console.log('Environment: ' + (process.env.APP_ENV || 'Not set'));
+}

lib/express.js

@@ -79,3 +79,9 @@ exports.raw = bodyParser.raw
 exports.static = require('serve-static');
 exports.text = bodyParser.text
 exports.urlencoded = bodyParser.urlencoded
+
+/**
+ * Expose utilities.
+ */
+
+exports.loadEnv = require('./utils').loadEnv;