Test if ES6 is ~fully supported

supportsES6.js

var supportsES6 = function() {
  try {
    new Function("(a = 0) => a");
    return true;
  }
  catch (err) {
    return false;
  }
}();

@triblondon Yup, the critical test is the a = 0 (all browsers supporting default parameters have a fairly complete support of ES6 -- for example, Edge 13 will be rejected by this test despite a decent ES6 coverage).

I wanna know how to prove “all browsers supporting default parameters have a fairly complete support of ES6”
Thankfully， if you can show links or refs