window.fetch polyfill vs ky
Which should you use? A side-by-side look at what each one does, who it suits, what it costs, how hard it is to set up, and where each falls short.
Open source · MIT
A browser polyfill that adds window.fetch to older browsers that lack it.
Open source · MIT
A tiny HTTP client for JavaScript that wraps the Fetch API with simpler calls and error handling.
The short answer
Choose window.fetch polyfill if you need…
- Front-end developers maintaining web apps that must support older browsers
- Teams replacing XMLHttpRequest code with a Promise-based API
- Projects that import a package and want window.fetch available automatically
Choose ky if you need…
- JavaScript or TypeScript developers who already use fetch and want less boilerplate
- Projects that call a REST API and want JSON parsing and error handling in one call
- Developers who want a small package with no dependencies
- Teams that want typed responses or validation with Zod or Valibot via Standard Schema
Side-by-side
| window.fetch polyfill | ky | |
|---|---|---|
| Type | Library | Library |
| Price | Free and open source | Free and open source |
| Licence | MIT | MIT |
| GitHub stars | 25.8k | 17.1k |
| Setup difficulty | Beginner | Beginner |
| How you get it | Install with a package manager | Install with a package manager |
| Main language | JavaScript | TypeScript |
| Last code update | 2 years ago | 28 days ago |
What each one is
window.fetch polyfill
This project provides a fetch() function for making web requests from JavaScript in the browser, for browsers that do not support fetch natively. It implements a subset of the Fetch specification so it can replace most XMLHttpRequest uses in traditional web apps. The README notes that modern browsers already have fetch built in, so the code has no effect there.
ky
Ky is a small JavaScript library for making HTTP requests, such as loading data from or sending data to a web server. It builds on the browser's built-in fetch function and adds conveniences like JSON handling, automatic retries, timeouts, and treating error status codes as errors. The README says it has no dependencies and works in modern browsers, Node.js, Bun, and Deno.
Best for
window.fetch polyfill
- Front-end developers maintaining web apps that must support older browsers
- Teams replacing XMLHttpRequest code with a Promise-based API
- Projects that import a package and want window.fetch available automatically
ky
- JavaScript or TypeScript developers who already use fetch and want less boilerplate
- Projects that call a REST API and want JSON parsing and error handling in one call
- Developers who want a small package with no dependencies
- Teams that want typed responses or validation with Zod or Valibot via Standard Schema
Strengths
window.fetch polyfill
- Small, focused drop-in that follows the Fetch specification API
- MIT licensed and widely used, with about 25.8k GitHub stars
- README gives clear examples for common tasks like JSON, forms, and uploads
ky
- Small package with no dependencies, according to the README
- Adds retries, timeouts, hooks, and error handling on top of plain fetch
- Typed responses: .json() defaults to unknown rather than any
Not ideal for
window.fetch polyfill
- Modern-browser-only projects, because native fetch already exists and the polyfill does nothing there
- Node.js or server-side code, because the README says it does not work under Node.js
- Apps needing redirect modes, cache options, or keepalive, because the README says these are ignored or unsupported
ky
- People who are not writing JavaScript or TypeScript code, since this is a code library
- Projects that need a feature the README does not mention, such as a built-in cookie jar, because the README does not cover that
- Anyone needing to support environments without fetch support, since Ky is built on the Fetch API
Trade-offs
window.fetch polyfill
- Only implements a subset of the Fetch spec; redirect and cache options are ignored
- Needs a separate Promise polyfill for older browsers, and CORS and cookie behavior depend on the browser
- Browser-only; the README says it does not work under Node.js
ky
- Requires a runtime with fetch support, so it is not a fit for older environments
- The README describes the next version of Ky, so the docs may differ from the version most people install
- Some features, such as streaming request bodies, depend on browser support the README describes as limited
Getting started
window.fetch polyfill
Install the package
npm install whatwg-fetch --saveFrequently asked questions
What is the difference between window.fetch polyfill and ky?
window.fetch polyfill: A browser polyfill that adds window.fetch to older browsers that lack it. ky: A tiny HTTP client for JavaScript that wraps the Fetch API with simpler calls and error handling. window.fetch polyfill suits front-end developers maintaining web apps that must support older browsers, while ky suits javascript or typescript developers who already use fetch and want less boilerplate.
Are window.fetch polyfill and ky free?
window.fetch polyfill: Free and open source. ky: Free and open source.
Is window.fetch polyfill or ky more popular?
window.fetch polyfill has more GitHub stars (25.8k) than ky (17.1k). Popularity isn't the same as fit — check which one matches your use case above.
What are other alternatives to window.fetch polyfill and ky?
Other options people compare them with include axios, got, core-js, TanStack Query, SwiftyJSON.
Keep comparing
Built from our catalogue entries for both products: open-source details come from each project's README (AI-assisted, refreshed weekly) and GitHub data; AI-tool details are editorial. Spotted something wrong? Let us know from either product's page.