Function qualified_name 

pub fn qualified_name(
    js_namespace: Option<&[impl AsRef<str>]>,
    js_name: &str,
) -> String

Compute a “qualified name” by prepending the namespace (joined with __) to the js_name. When there is no namespace, this returns the js_name unchanged. This is used to disambiguate internal wasm symbols when the same js_name appears in different namespaces. __ is used as the separator because double underscores are unlikely to appear in user-defined names.