WASM-HXR example is using `Fetch API`

[smoyer64]

In your WASM-XHR example at https://github.com/siongui/frontend-programming-in-go/blob/master/wasm/005-xmlhttprequest-xhr/xhr.go#L10, this call is actually using the Fetch API under the covers, not XMLHTTPRequest (tested on modern Chromium, FireFox and Safari ... this may have changed since you published the example.)