How to detect the return type in actionscript

I have a an event handler (event:ResultEvent) that could return 1 of 2 types. Does actionscript3 have a function to test the type returned? something like

if (type(event.result) == ProxyObject) {
  // do开发者_开发知识库 something
} else {
  // do something else
}

You should be able to use

if (event.result is ProxyObject) {}

More details are here.