Node与React中import *的最佳实践及导入体积影响问询

Great question—let’s break down when to use (and avoid) import * syntax, along with clear answers to your specific concerns about Express, local modules, and bundle size.

When import * Makes Sense #

• For namespace organization: If you’re working with a module that exports many related functions/values (like a utility library or SDK), wrapping them in a single namespace keeps your code clean and avoids cluttering the top-level scope. For example:

  import * as mathUtils from './math-utils';
  // Use like mathUtils.add(), mathUtils.multiply()
  

• For broad, frequent module usage: If you need almost every export from a module, listing them all individually would be tedious. import * is a reasonable shortcut here—just ensure the module is small enough that this doesn’t hurt code readability.

When to Skip import * #

• React components and explicit API usage: In React, it’s far better to import only the hooks/components you need. Instead of import * as React from 'react', use:

  import { useState, useEffect } from 'react';
  

  This makes it immediately clear which React APIs your component depends on, and aligns with community best practices (plus, React 17+ supports automatic imports for core APIs anyway).
• Default-export heavy modules: Frameworks like Express rely heavily on default exports. import * as express from 'express' will work, but forces you to call express.default() to initialize the app—whereas the standard import express from 'express' lets you call express() directly. It’s unnecessary extra code, so stick to default imports here.

Does import * Bloat Your Bundle Size? #

Short answer: It depends on your tooling and module type:

• ES Modules (ESM) + Tree-Shaking: If your module uses modern ESM syntax and you’re using a bundler like Webpack, Vite, or Rollup with tree-shaking enabled, unused exports from import * will be stripped out. Your final bundle won’t include code you don’t actually use.
• CommonJS Modules: Older Node.js packages or local files using CommonJS (e.g., module.exports) can’t be tree-shaken reliably, since CommonJS is dynamic. In this case, import * might pull in more code than you need.
• Side Effects: Even with tree-shaking, if a module has exports with side effects (like modifying global variables), those might not be stripped—so explicit imports are safer to avoid unintended behavior.

Your Specific Examples #

• import * from 'express': As mentioned, this is not ideal. Express’s main functionality is exposed via its default export, so use import express from 'express' instead. If you need additional exports like Router, add them explicitly:

  import express, { Router } from 'express';
  

• import * from './../../myCode': First, note that valid syntax requires an alias: import * as myCode from './../../myCode'. This is acceptable if you need most of the module’s exports, but if you only use a handful of functions, list them explicitly to improve readability and reduce any potential bundle bloat (even if tree-shaking handles it).

Final Takeaways #

• Use import * for namespace clarity or when you need most of a module’s exports.
• Prefer explicit named/default imports for better readability and to avoid unnecessary code (especially in React and with frameworks like Express).
• Bundle size concerns are mostly mitigated with modern ESM and tree-shaking, but explicit imports are still the safer, more readable choice.

内容的提问来源于stack exchange，提问作者Hello-World