Chrome javascript Proxy object is not defined
if you’re using Chrome most of the ES6 features are hidden behind a feature toggle. Browse to chrome://flags, find the section titled “Enable Experimental JavaScript” and enable it to turn on support: chrome://flags/#enable-javascript-harmony
After activation, restart your chrome browser and it should work
V8 released full support for Proxy in 4.9
Source; http://v8project.blogspot.de/2016/01/v8-release-49.html
Chrome 49 uses V8 4.9
Just start chrome from command line with flag --js-flags="--harmony-proxies" or add it to chrome's shortcut