attempt fixing parseBody

- why?
when using the mixfetch SDK, i was encountering issues, when posting requests to specific endpoints. It was not parsing the response correctly with:

Error: panic:syscall/js: Value.Call: property getReader is not a function

By updating the above, i've tested this works on all variations of post and get request using mixfetch.

Locally I had to upgrade my version of go to 1.20

wasm/mix-fetch/go-mix-conn/internal/jstypes/conv/request.go

@@ -223,13 +223,20 @@ func parseHeaders(headers js.Value, reqOpts types.RequestOptions, method string)
 func parseBody(request *js.Value) (io.Reader, error) {
 	jsBody := request.Get(fieldRequestBody)
 	var bodyReader io.Reader
+
 	if !jsBody.IsUndefined() && !jsBody.IsNull() {
-		log.Debug("stream body - getReader")
-		bodyReader = external.NewStreamReader(jsBody.Call("getReader"))
+		// Check to see if getReader is a function
+		if jsBody.InstanceOf(js.Global().Get("ReadableStream")) && jsBody.Get("getReader").Type() == js.TypeFunction {
+			log.Debug("stream body - getReader")
+			bodyReader = external.NewStreamReader(jsBody.Call("getReader"))
+		} else {
+			// Fall back to using ArrayBuffer
+			// https://developer.mozilla.org/en-US/docs/Web/API/Body/arrayBuffer
+			log.Debug("getReader not available - fallback to ArrayBuffer")
+			bodyReader = external.NewArrayReader(request.Call("arrayBuffer"))
+		}
 	} else {
-		log.Debug("unstremable body - fallback to ArrayBuffer")
-		// Fall back to using ArrayBuffer
-		// https://developer.mozilla.org/en-US/docs/Web/API/Body/arrayBuffer
+		log.Debug("unstreamable body - fallback to ArrayBuffer")
 		bodyReader = external.NewArrayReader(request.Call("arrayBuffer"))
 	}
 
@@ -237,9 +244,11 @@ func parseBody(request *js.Value) (io.Reader, error) {
 	if err != nil {
 		return nil, err
 	}
+	// Leaving historical notes as reference points
 	// TODO: that seems super awkward. we're constructing a reader only to fully consume it
 	// and create it all over again so that we the recipient wouldn't complain about content-length
 	// surely there must be a better way?
+
 	return bytes.NewReader(bodyBytes), nil
 }