[CharlesW]

It currently scores 96.8% on the ES6 Compatibility Table hosted by kangax[1], which is pretty good. That's native, no polyfills or transpiler.

EDIT: Kinoma claims ES6 compatibility is at 98% as of 2016-01-02.[2]

[1] https://kangax.github.io/compat-table/es6/ [2] http://www.kinoma.com/develop/documentation/js6/