ah slight snag, turns out that apply is also throwing the error
Class constructors cannot be invoked without 'new' in current chome canary.
Caitlin quotes in the esdicuss topic:
People are experimenting with polyfilled class implementations, which don’t all correctly throw when called as a function (no new). Eventually, they’re likely to be disappointed that this isn’t legal, and might have to undergo some serious pains to fix their applications.
But yeah we should be ok because when it's ES6 proper we shouldn't be affected because we will no longer be using a polyfill. Nor are we calling call\apply on classes directly.