var objectProxy = new Proxy({}, {}); var functionProxy = new Proxy(function() {}, {}); assertEq(Object.prototype.toString.call(objectProxy), '[object Object]'); assertEq(Object.prototype.toString.call(functionProxy), '[object Function]'); try { Function.prototype.toString.call(objectProxy); assertEq(true, false); } catch (e) { assertEq(!!/incompatible/.exec(e), true); }