Node.js模块导入时大括号的使用场景及require与ES6规则差异

Great question—this is a super common point of confusion between Node.js's traditional CommonJS require syntax and ES6 module imports. Let's break this down clearly:

First: The Key Difference Between the Two Curly Brace Uses #

These two syntaxes look identical, but they operate under totally different rules:

• ES6 import { ... } is part of the native module import system, specifically built to pull in named exports from a module.
• Curly braces paired with require are actually ES6 object destructuring—a general JavaScript feature, not something unique to the require function itself.

When to Use Curly Braces with require #

You’ll reach for curly braces here when the module you’re importing exports an object with multiple properties or methods, and you only need to grab one (or a few) specific properties from that object.

For example, if your ./db/mongoose.js file exports like this:

// ./db/mongoose.js
const mongoose = require('mongoose');
// Export an object that contains the mongoose instance plus other utilities
module.exports = { mongoose, dbConnectionHelper };

Using const { mongoose } = require('./db/mongoose.js') is just a shortcut to extract the mongoose property directly from the exported object, instead of writing:

const dbModule = require('./db/mongoose.js');
const mongoose = dbModule.mongoose;

If the module exports a single standalone value (like most core Node.js modules or the main mongoose package), you don’t need curly braces at all. For example:

// The official mongoose module exports the mongoose class directly as its main export
const mongoose = require('mongoose');

How This Compares to ES6 import #

With ES6 modules, the curly braces are tightly linked to how the module exports values:

• Use import { mongoose } from './db/mongoose.js' when the module uses a named export:

  // ./db/mongoose.js (ES6 module)
  export const mongoose = require('mongoose');
  

• Use import mongoose from './db/mongoose.js' when the module uses a default export:

  // ./db/mongoose.js (ES6 module)
  export default require('mongoose');
  

Unlike with require, the curly braces here aren’t just a shortcut—they’re part of the import syntax that tells JavaScript exactly which named export you want to pull in.

Quick Cheat Sheet #

• No curly braces with require: When the module exports a single value (class, function, or single object).
• Curly braces with require: When the module exports an object with multiple properties, and you want to extract specific ones (this is object destructuring).
• ES6 import curly braces: Exclusively for importing named exports from ES6 modules.

内容的提问来源于stack exchange，提问作者Prem