Math.round issues

[Yaffle]

see https://twitter.com/BrendanEich/status/360832908514181122

Math.round(0.5 - Number.EPSILON / 4) should be equal to 0

Math.round((2 / Number.EPSILON + 1) / 2 + 1) should be equal to (2 / Number.EPSILON + 1) / 2 + 1
Math.round(2 / Number.EPSILON) should be equal to 2 / Number.EPSILON

The ES5 spec - http://es5.github.io/#x15.8.2.15 - says, that Math.round "Returns the Number value that is closest to x and is equal to a mathematical integer", but Note 2 says nothing about
Note 2 was fixed in ES6 - https://people.mozilla.org/~jorendorff/es6-draft.html#sec-math.round

Some browsers have good implementaions (FF 35, Chrome ?):
https://bugzilla.mozilla.org/show_bug.cgi?id=622348
https://bugzilla.mozilla.org/show_bug.cgi?id=1000606

But IE 11, Opera 12, Safari are buggy here.

I think, the implementation may look like this:

Math.round = function (x) {
  var n = Number(x);
  var ceil = Math.ceil(n);
  return ceil  - (ceil - 0.5 > n ? 1 : 0);
};

[ljharb]

Addressed by es-shims/es6-shim@90c803f

[ljharb]

Sorry, that was in the es6-shim. The es5 parts need to be addressed here.