仅为类型声明导入模块是否成本高昂？用express类型替代any是否推荐？

Question 1: Does importing modules solely for type declarations incur high costs? #

Great question—this is a common concern when working with TypeScript, but the short answer is no, not if you do it correctly.

TypeScript has a dedicated syntax for importing only types: import type. When you use this syntax (e.g., import type { Response } from 'express'), the TypeScript compiler knows to completely strip these imports during compilation. That means there's zero runtime overhead—no extra code is bundled, no module is loaded at runtime just for types.

If you accidentally use a regular import for a type (like import { Response } from 'express') without actually using any runtime values from the module, most modern bundlers (Webpack, Vite, Rollup) will still tree-shake the unused import. However, using import type is the safer, more explicit approach. It makes your intent clear to both other developers and the compiler, so there's no chance of unintended runtime imports slipping through.

Question 2: Is it recommended to use types like express.Response instead of any? #

Absolutely—this is exactly what TypeScript is designed for, and it's a best practice you should follow whenever possible.

Using any turns off TypeScript's type checking entirely. This means you lose all the benefits of TypeScript: autocompletion for methods on Response (like res.json() or res.status()), compile-time error checking (e.g., catching typos like res.sendd() before your code runs), and improved code readability for other developers who can immediately see what type of value a variable should be.

To use express.Response without runtime overhead, just use a type-only import:

import type { Response } from 'express';

function handleRequest(res: Response) {
  res.status(200).json({ message: 'Success' });
  // TypeScript will catch errors here, like if you try res.invalidMethod()
}

Avoiding any makes your code more robust, easier to maintain, and reduces the chance of bugs making it to production. The only time you might need to use any is if you're dealing with a dynamic value that you truly can't type (and even then, consider using unknown instead, which forces you to narrow the type before using it).

内容的提问来源于stack exchange，提问作者u936293