Current proposal, subject to change

Feature name Current browser Traceur 6to5 +
polyfill
[1]
IE 11 FF 31 FF 32 FF34 FF35 CH 30[1] CH 33[1] CH 34[1] CH 35[1] CH 37[1] SF 7, SF 8 WK KQ 4.13 RH PH Node Node harmony[2] Echo JS iOS7 iOS8
§Exponentiation operator Yes Yes No No No Yes Yes No No No No No No No No No No No No No No No
§Array comprehensions Yes Yes No Yes Yes Yes Yes No No No No No No No No No No No No No No No
§Generator comprehensions Yes Yes No Yes Yes Yes Yes No No No No No No No No No No No No No No No
§Typed objects No No No No No Yes Yes No No No No No No No No No No No No No No No
§Object.observe No No No No No No No No Yes Yes Yes Yes No No No No No No Yes No No No
§Object.getOwnPropertyDescriptors No No No No No No No No No No No No No No No No No No No No No No
§Array.prototype.contains No No No No No No Yes[3] No No No No No No No No No No No No No No No
§Reflect.Realm No No No No No No No No No No No No No No No No No No No No No No

[1] Have to be enabled via "Experimental Javascript features" flag

[2] Have to be enabled via --harmony flag

[3] Only enabled in Nightly builds