# Is resize-observer-polyfill ESM-only? Can you require() it?

> resize-observer-polyfill@1.5.1 is a CommonJS package. CommonJS — require() works on every Node.js version we test.

A polyfill for the Resize Observer API

Last verified Sep 9, 2026 against resize-observer-polyfill@1.5.1.

resize-observer-polyfill ships CommonJS only. require("resize-observer-polyfill") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. import "resize-observer-polyfill" 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("resize-observer-polyfill") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun.
2. From ES modules use the default import: import resizeObserverPolyfill from "resize-observer-polyfill"; then destructure. Named imports only work when Node.js can statically detect the exports.
3. TypeScript: types are bundled; install nothing extra.

## Facts

- Latest: 1.5.1 (Dec 9, 2018)
- Module format: CommonJS
- Last CommonJS version: 1.5.1
- TypeScript types: bundled
- Node engines: not declared
- Weekly downloads: 12.7M
- License: MIT

## Runtime test results for resize-observer-polyfill@1.5.1

Installed and executed on Sep 9, 2026 with require("resize-observer-polyfill") from a CommonJS file and import "resize-observer-polyfill" from an ES module.

| Runtime | require("resize-observer-polyfill") | import "resize-observer-polyfill" |
|---|---|---|
| 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 resize-observer-polyfill

ES modules:

```js
import resizeObserverPolyfill from "resize-observer-polyfill";
```

CommonJS:

```js
const resizeObserverPolyfill = require("resize-observer-polyfill");
```

## Module format by version

Derived from the type, main and exports fields of every stable release on npm (17 versions; the newest 17 shown).

| Versions | Format | First published |
|---|---|---|
| 1.0.0 – 1.5.1 | CommonJS | Sep 12, 2016 |

## Frequently asked

**Is resize-observer-polyfill ESM-only?**

resize-observer-polyfill@1.5.1 is a CommonJS package. resize-observer-polyfill ships CommonJS only. require("resize-observer-polyfill") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. import "resize-observer-polyfill" 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 resize-observer-polyfill with ES module syntax?**

Yes. import resizeObserverPolyfill from "resize-observer-polyfill" 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 resize-observer-polyfill work in Bun?**

Yes. import "resize-observer-polyfill" loaded successfully in Bun 1.4.0 on Sep 9, 2026.

**Does resize-observer-polyfill ship TypeScript types?**

Yes. resize-observer-polyfill bundles its own type declarations; no @types package is needed.

## Links

- [resize-observer-polyfill on npm](https://www.npmjs.com/package/resize-observer-polyfill)
- [Source repository](https://github.com/que-etc/resize-observer-polyfill)
- [HTML version](https://canirequire.com/package/resize-observer-polyfill/)
- [JSON version](https://canirequire.com/package/resize-observer-polyfill.json)

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