如何解决Node.js中出现的“TypeError: connectDB is not a function”错误？

Hey there! Let's get this sorted out—this is a super common typo that trips up a lot of developers when working with Node.js modules.

The Problem Breakdown #

You're getting this error when calling connectDB() in your server.js:

TypeError: connectDB is not a function
    at Object.<anonymous> (C:\Users\rodri\flutter_auth\server.js:9:1)
    at Module._compile (node:internal/modules/cjs/loader:1105:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
    at node:internal/main/run_main_module:17:47

Looking at your code, the issue is hiding in your db.js file. Here's the relevant code for context:

server.js

const express = require('express');
const morgan = require('morgan');
const cors = require('cors');
const connectDB = require('./config/db');
const passport = require('passport');
const bodyParser = require('body-parser');

connectDB(); // This line throws the error

const app = express();

if (process.env.NODE_ENV === 'development') {
  app.use(morgan('dev'));
}

const PORT = process.env.PORT || 3000;

app.listen(PORT, console.log(`Server running in ${process.env.NODE_ENV} mode on port ${PORT}`));

db.js

const mongoose = require('mongoose');
const dbConfig = require('./dbconfig');

const connectDB = async () => {
  try {
    const conn = await mongoose.connect(dbConfig.database, {
      useNewUrlParser: true,
      useUnifiedTopology: true,
      useFindAndModify: false
    });
    console.log(`MongoDB Connected: ${conn.connection.host}`);
  } catch (err) {
    console.log(err);
    process.exit(1);
  }
};

// ❌ This is the mistake!
module.export = connectDB;

Why This Happens #

Node.js uses module.exports (notice the s at the end) to export values from a module. You wrote module.export (missing the s), which means you're not actually exporting your connectDB function. Instead, when you require('./config/db') in server.js, you're getting the default empty object instead of your function—hence the "not a function" error.

The Fix #

Simply correct the typo in db.js by adding the missing s:

// ✅ Correct export syntax
module.exports = connectDB;

Save the file, restart your server, and your Mongoose connection should work as expected!

内容的提问来源于stack exchange，提问作者pomoworko.com