# Is @smithy/middleware-stack ESM-only? Can you require() it?

> @smithy/middleware-stack@4.5.2 is a CommonJS package. CommonJS — require() works on every Node.js version we test.

Provides a means for composing multiple middleware functions into a single handler

Last verified Sep 9, 2026 against @smithy/middleware-stack@4.5.2.

@smithy/middleware-stack ships CommonJS only. require("@smithy/middleware-stack") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. The package declares Node.js >=18.0.0. import "@smithy/middleware-stack" also works because Node.js and Bun can import CommonJS from ES modules, but only the default export is guaranteed; named imports depend on Node's static analysis of the module.

It also declares a "module" field, so bundlers such as webpack, Vite and esbuild pick up an ESM build for tree-shaking.

## What to do

1. require("@smithy/middleware-stack") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. The package declares Node.js >=18.0.0.
2. From ES modules use the default import: import middlewareStack from "@smithy/middleware-stack"; then destructure. Named imports only work when Node.js can statically detect the exports.
3. TypeScript: types are bundled; install nothing extra.

## Facts

- Latest: 4.5.2 (Aug 15, 2026)
- Module format: CommonJS
- Last CommonJS version: 4.5.2
- TypeScript types: bundled
- Node engines: >=18.0.0
- Weekly downloads: 35.1M
- License: Apache-2.0

## Runtime test results for @smithy/middleware-stack@4.5.2

Installed and executed on Sep 9, 2026 with require("@smithy/middleware-stack") from a CommonJS file and import "@smithy/middleware-stack" from an ES module.

| Runtime | require("@smithy/middleware-stack") | import "@smithy/middleware-stack" |
|---|---|---|
| Node.js 18 | works | works |
| Node.js 20 | works | works |
| Node.js 22 | works | works |
| Node.js 24 | works | works |
| Node.js 26 | works | works |
| Bun 1.4.0 | works | works |

## How to import @smithy/middleware-stack

ES modules:

```js
import middlewareStack from "@smithy/middleware-stack";
```

CommonJS:

```js
const middlewareStack = require("@smithy/middleware-stack");
```

## Module format by version

Derived from the type, main and exports fields of every stable release on npm (84 versions; the newest 60 shown).

| Versions | Format | First published |
|---|---|---|
| 3.0.3 – 4.5.2 | CommonJS | Jun 27, 2024 |

## Frequently asked

**Is @smithy/middleware-stack ESM-only?**

@smithy/middleware-stack@4.5.2 is a CommonJS package. @smithy/middleware-stack ships CommonJS only. require("@smithy/middleware-stack") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. The package declares Node.js >=18.0.0. import "@smithy/middleware-stack" also works because Node.js and Bun can import CommonJS from ES modules, but only the default export is guaranteed; named imports depend on Node's static analysis of the module.

**Can I import @smithy/middleware-stack with ES module syntax?**

Yes. import middlewareStack from "@smithy/middleware-stack" works in Node.js and Bun because they support importing CommonJS modules. Named imports work only when Node.js can statically detect the exports.

**Does @smithy/middleware-stack work in Bun?**

Yes. import "@smithy/middleware-stack" loaded successfully in Bun 1.4.0 on Sep 9, 2026.

**Does @smithy/middleware-stack ship TypeScript types?**

Yes. @smithy/middleware-stack bundles its own type declarations; no @types package is needed.

## Links

- [@smithy/middleware-stack on npm](https://www.npmjs.com/package/@smithy/middleware-stack)
- [Source repository](https://github.com/smithy-lang/smithy-typescript)
- [HTML version](https://canirequire.com/package/@smithy/middleware-stack/)
- [JSON version](https://canirequire.com/package/@smithy/middleware-stack.json)

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