toJSProxyOrRef property
Either passes by reference, unwraps, or creates a heavyweight proxy that wraps the list.
Only use this member if you want modifications to the list to also affect the JS array and vice versa. In practice, dart2js and DDC will pass lists by reference and dart2wasm will add a proxy or unwrap for most lists.
WARNING: Do not rely on this to be performant.
Implementation
external JSArray<T> get toJSProxyOrRef;