Emscripten provides a Fetch API as well. The following is taken from the documentation:
"The Emscripten Fetch API allows native code to transfer files via XHR (HTTP GET, PUT, POST) from remote servers, and to persist the downloaded files locally in browser's IndexedDB storage, so that they can be re-accessed locally on subsequent page visits. The Fetch API is callable from multiple threads, and the network requests can be run either synchronously or asynchronously as desired."
The Fetch API can be used to integrate with Emscripten's other features. If you need to fetch data that isn't utilized by Emscripten, you should use the browser's Fetch API (https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API). You can read more about the Fetch API at https://kripken.github.io/emscripten-site/docs/api_reference/fetch.html.