This is a problem with the Chrome devtools console, which is trying to show the result, not the Proxy constructor itself. What version of Chrome are you using?
In the Chrome 50 console, I see the following:
> let p = new Proxy(function(){return 6},{})
< undefined
> p
<
Uncaught illegal access
DebuggerScript.getFunctionScopes @ (program):4
> p()
< 6
, proxy , barfs . Chrome. .