syscall/js: add a note about a bug in TypedArray

Fixes #29355

Change-Id: I4018d420c8d413b2681744af18ffb65da03ac504
Reviewed-on: https://go-review.googlesource.com/c/155778
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Richard Musiol <neelance@gmail.com>

src/syscall/js/typedarray.go

@@ -25,6 +25,11 @@ var (
 var _ Wrapper = TypedArray{} // TypedArray must implement Wrapper
 
 // TypedArray represents a JavaScript typed array.
+//
+// BUG(neelance): The typed array currently becomes inaccessible when Go requests more memory
+// from the WebAssembly host. It is recommended to only use the typed array synchronously
+// without keeping a long-lived reference. You can also check if the length property is zero
+// to detect this detached state of the typed array.
 type TypedArray struct {
 	Value
 }