V8 SpiderMonkey JavaScriptCore Chakra Other
Minor difference (1 point) Small feature (2 points) Medium feature (4 points) Large feature (8 points)
Feature name Current browser Traceur Babel +
core-js
[2]
Closure Type-
Script +
core-js
es7-shim IE 9 IE 10 IE 11 Edge 12[3] Edge 13[3] Edge 14[3] Edge 15[3] FF 38 ESR FF 45 ESR FF 46 FF 47 FF 48 FF 49 FF 50 FF 51 FF 52 ESR FF 53 FF 54 Beta FF 55 Nightly CH 50,
OP 37
[1]
CH 51,
OP 38
[1]
CH 52,
OP 39
[1]
CH 53,
OP 40
[1]
CH 54,
OP 41
[1]
CH 55,
OP 42
[1]
CH 56,
OP 43
[1]
CH 57,
OP 44
[1]
CH 58,
OP 45
[1]
CH 59,
OP 46
[1]
CH 60,
OP 47
[1]
SF 8 SF 9 SF 10 SF 10.1 SF TP WK PJS Node 0.10[4] Node 0.12[4] io.js[4] Node 4[4] Node 5[4] Node 6.0-6.4[4] Node >=6.5 <7[4] Node 7.0-7.5[4] Node >=7.6 <8[4] DUK 2.0 DUK 2.1 AN 4.0 AN 4.1 AN 4.2 AN 4.3 AN 4.4 AN 5.0 AN 5.1 iOS 8 iOS 9 iOS 10.0-10.2 iOS >=10.3 <11
2016 features
§exponentiation (**) operator MDN (Mozilla Development Network) logo  2/3 3/3 3/3 2/3 0/3 0/3 0/3 0/3 0/3 0/3 3/3 3/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 3/3 3/3 3/3 3/3 0/3 0/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 0/3 0/3 0/3 3/3 3/3 3/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 3/3 3/3 2/3 2/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 3/3
§basic support Yes Yes Yes Yes No No No No No Flag Yes Yes No No[5] No[5] No[5] No[5] No[5] No[5] No[5] Yes Yes Yes Yes No Flag Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No Flag Yes Yes Yes Yes No No No No No No No No No No Yes
§assignment Yes Yes Yes Yes No No No No No Flag Yes Yes No No No No No[5] No[5] No[5] No[5] Yes Yes Yes Yes No Flag Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No Flag Yes Yes Yes Yes No No No No No No No No No No Yes
§early syntax error for unary negation without parens No Yes Yes No No No No No No No Yes Yes No No No No No No No No Yes Yes Yes Yes No Flag Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No Flag Yes Yes No No No No No No No No No No No No Yes
§Array.prototype.includes MDN (Mozilla Development Network) logo  0/3 3/3 0/3 3/3 2/3 0/3 0/3 0/3 0/3 0/3 3/3 3/3 0/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 0/3 2/3 3/3 3/3 3/3 3/3 0/3 0/3 0/3 0/3 0/3 0/3 3/3 3/3 3/3 3/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 2/3 3/3 3/3
§Array.prototype.includes MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes No No No No No Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes No No No No No No No No No No Yes Yes Yes
§Array.prototype.includes is generic No Yes No Yes[6] Yes No No No No No Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes No No No No No No No No No No Yes Yes Yes
§%TypedArray%.prototype.includes MDN (Mozilla Development Network) logo  No Yes No Yes[6] No No No No No No Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes No No No No No No No No No No No Yes Yes
2016 misc
§generator functions can't be used with "new" MDN (Mozilla Development Network) logo [7] No No No No No No No No No Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes No No No No No No No No No No No Yes Yes
§generator throw() caught by inner generator MDN (Mozilla Development Network) logo [8] No No Yes No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No Flag Flag Yes Yes Yes Yes Yes Yes No No No No No No No No Yes No No Yes Yes
§strict fn w/ non-strict non-simple params is error[9] No No No No No No No No Yes Yes Yes Yes No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes No No No No No No No No No No No Yes Yes
§nested rest destructuring, declarations MDN (Mozilla Development Network) logo [10] No Yes Yes Yes No No No No No Flag Yes Yes No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No Yes Yes Yes Yes No No No No No No No No No No No No Yes
§nested rest destructuring, parameters[11] No Yes Yes Yes No No No No No Flag Yes Yes No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No Yes Yes Yes Yes No No No No No No No No No No No No Yes
§Proxy, "enumerate" handler removed MDN (Mozilla Development Network) logo [12] No No No No No No No No No No No Yes No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes Yes No No No No No No No No No Yes Yes
§Proxy internal calls, Array.prototype.includes No No No No No No No No No No Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes No No No No No No No No No No No Yes Yes
2017 features
§Object static methods 0/4 3/4 0/4 3/4 3/4 0/4 0/4 0/4 0/4 0/4 2/4 4/4 0/4 0/4 0/4 2/4 2/4 2/4 4/4 4/4 4/4 4/4 4/4 4/4 0/4 0/4 0/4 0/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 0/4 0/4 1/4 4/4 4/4 4/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 4/4 4/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 1/4 4/4
§Object.values MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes No No No No No Yes Yes No No[5] No[5] Yes Yes Yes Yes Yes Yes Yes Yes Yes No Flag Flag Flag Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No Flag Yes Yes No No No No No No No No No No No No Yes
§Object.entries MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes No No No No No Yes Yes No No[5] No[5] Yes Yes Yes Yes Yes Yes Yes Yes Yes No Flag Flag Flag Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No Flag Yes Yes No No No No No No No No No No No No Yes
§Object.getOwnPropertyDescriptors MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes No No No No No No Yes No No No No No No Yes Yes Yes Yes Yes Yes No Flag Flag Flag Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No No Flag Yes Yes No No No No No No No No No No No Yes Yes
§Object.getOwnPropertyDescriptors doesn't provide undefined descriptors No No No No No No No No No No No Yes No No No No No No Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No Yes Yes No No No No No No No No No No No No Yes
§String padding 0/2 2/2 0/2 2/2 2/2 0/2 0/2 0/2 0/2 0/2 0/2 2/2 0/2 0/2 0/2 0/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 2/2 2/2 2/2 2/2 0/2 0/2 2/2 2/2 2/2 2/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 2/2 2/2
§String.prototype.padStart MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes No No No No No Flag Yes No No No No Yes Yes Yes Yes Yes Yes Yes Yes No No Flag Flag Flag Flag Flag Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No No No Flag Flag No No No No No No No No No No No Yes Yes
§String.prototype.padEnd MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes No No No No No Flag Yes No No No No Yes Yes Yes Yes Yes Yes Yes Yes No No Flag Flag Flag Flag Flag Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No No No Flag Flag No No No No No No No No No No No Yes Yes
§trailing commas in function syntax MDN (Mozilla Development Network) logo  0/2 2/2 0/2 2/2 0/2 0/2 0/2 0/2 0/2 0/2 2/2 2/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 2/2 2/2 2/2 2/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 2/2 2/2 2/2 0/2 0/2 2/2 2/2 2/2 2/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 2/2 2/2
§in parameter lists MDN (Mozilla Development Network) logo  No Yes No Yes No No No No No No Yes Yes No No No No No No No No Yes Yes Yes Yes No No No No No No No Flag Yes Yes Yes No No Yes Yes Yes Yes No No No No No No No No No No No No No No No No No No No No No Yes Yes
§in argument lists MDN (Mozilla Development Network) logo  No Yes No Yes No No No No No No Yes Yes No No No No No No No No Yes Yes Yes Yes No No No No No No No Flag Yes Yes Yes No No Yes Yes Yes Yes No No No No No No No No No No No No No No No No No No No No No Yes Yes
§async functions MDN (Mozilla Development Network) logo  3/15 3/15 3/15 2/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 15/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 15/15 15/15 15/15 15/15 0/15 0/15 0/15 0/15 0/15 15/15 15/15 15/15 15/15 15/15 15/15 0/15 0/15 0/15 15/15 15/15 15/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 15/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 15/15
§return Yes Yes[13] Yes Yes[14] No No No No No Flag Flag Yes No No No No No No No No Yes Yes Yes Yes No No Flag Flag Flag Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No Flag Yes No No No No No No No No No No No No Yes
§throw ? ? ? ? No No No No No Flag Flag Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§no line break between async and function ? ? ? ? No No No No No No Flag Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§no "prototype" property ? ? ? ? No No No No No Flag Flag Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§await MDN (Mozilla Development Network) logo  Yes Yes[13] Yes Yes[14] No No No No No Flag Flag Yes No No No No No No No No Yes Yes Yes Yes No No Flag Flag Flag Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No Flag Yes No No No No No No No No No No No No Yes
§await, rejection ? ? ? ? No No No No No Flag Flag Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§must await a value ? ? ? ? No No No No No Flag Flag Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§can await non-Promise values ? ? ? ? No No No No No Flag Flag Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§cannot await in parameters ? ? ? ? No No No No No Flag Flag Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§async methods, object literals ? ? ? ? No No No No No Flag Flag Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§async methods, classes ? ? ? ? No No No No No Flag Flag Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§async arrow functions Yes Yes[13] Yes No No No No No No Flag Flag Yes No No No No No No No No Yes Yes Yes Yes No No Flag Flag Flag Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No Flag Yes No No No No No No No No No No No No Yes
§correct prototype chain ? ? ? ? No No No No No No Flag Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§async function prototype, Symbol.toStringTag ? ? ? ? No No No No No No No Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§async function constructor ? ? ? ? No No No No No No Flag Yes No No No No No No No No Yes Yes Yes Yes No No ? ? ? Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No ? Yes No No No No No No No No No No No No Yes
§shared memory and atomics 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 17/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 16/17 17/17 17/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 16/17
§SharedArrayBuffer MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§SharedArrayBuffer[Symbol.species] No No No No No No No No No No No Flag No No No No No No No No No[15] Flag[16] Flag[16] Yes No No No No No No No No No No No No No No Yes Yes Yes No No No No No No No No No No No No No No No No No No No No No No Yes
§SharedArrayBuffer.prototype.byteLength MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No No
§SharedArrayBuffer.prototype.slice MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No No No No No No No[15] Flag[16] Flag[16] Yes No No No No No No No No No No No No No No Yes Yes Yes No No No No No No No No No No No No No No No No No No No No No No Yes
§SharedArrayBuffer.prototype[Symbol.toStringTag] No No No No No No No No No No No Flag No No No No No No No No No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.add MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.and MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.compareExchange MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.exchange MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.wait MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No No No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.wake MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No No No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.isLockFree MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.load MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.or MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.store MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.sub MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
§Atomics.xor MDN (Mozilla Development Network) logo  No No No No No No No No No No No Flag No No No[5] No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No No No No No No No Yes
2017 misc
§Proxy "ownKeys" handler, duplicate keys for non-extensible targets MDN (Mozilla Development Network) logo  No No No No No No No No No No No No No No No No No No No Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes Yes No No No No No No No No No Yes Yes
§RegExp "u" flag, case folding No No No No No No No No No No No No No No No No No No No No No No Yes Yes No No No No No No No No No Yes Yes No No Yes Yes Yes Yes No No No No No No No No No No No No No No No No No No No No No Yes Yes
§arguments.caller removed MDN (Mozilla Development Network) logo  No No No No No No No No No No No No No No No No No No No No No Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes No No No Yes Yes Yes No No No No No No No No No No No No No No No No No No No No No No Yes
2017 annex b
§Object.prototype getter/setter methods 0/16 16/16 0/16 16/16 0/16 0/16 0/16 8/16 12/16 12/16 12/16 12/16 14/16 14/16 14/16 14/16 16/16 16/16 16/16 16/16 16/16 16/16 16/16 16/16 10/16 10/16 10/16 10/16 10/16 10/16 10/16 12/16 12/16 12/16 12/16 12/16 16/16 16/16 16/16 16/16 16/16 12/16 0/16 10/16 10/16 10/16 10/16 10/16 10/16 10/16 10/16 0/16 0/16 10/16 10/16 10/16 10/16 6/16 6/16 10/16 12/16 16/16 16/16 16/16
§__defineGetter__ MDN (Mozilla Development Network) logo  No Yes No Yes[6] No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__defineGetter__, symbols No Yes No Yes[6] No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No Yes No Yes Yes Yes
§__defineGetter__, ToObject(this) No Yes No Yes[6] No No No No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No No No No No No No No Yes Yes Yes Yes
§__defineSetter__ MDN (Mozilla Development Network) logo  No Yes No Yes[6] No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__defineSetter__, symbols No Yes No Yes[6] No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No Yes No Yes Yes Yes
§__defineSetter__, ToObject(this) No Yes No Yes[6] No No No No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No No No No No No No No Yes Yes Yes Yes
§__lookupGetter__ MDN (Mozilla Development Network) logo  No Yes No Yes[6] No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__lookupGetter__, prototype chain No Yes No Yes[6] No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__lookupGetter__, symbols No Yes No Yes[6] No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No Yes No Yes Yes Yes
§__lookupGetter__, ToObject(this) No Yes No Yes[6] No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No No No No No No No No Yes Yes Yes Yes
§__lookupGetter__, data properties can shadow accessors No Yes No Yes[6] No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No No No No No No No No Yes Yes Yes Yes
§__lookupSetter__ MDN (Mozilla Development Network) logo  No Yes No Yes[6] No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__lookupSetter__, prototype chain No Yes No Yes[6] No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__lookupSetter__, symbols No Yes No Yes[6] No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No Yes No Yes Yes Yes
§__lookupSetter__, ToObject(this) No Yes No Yes[6] No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No No No No No No No No Yes Yes Yes Yes
§__lookupSetter__, data properties can shadow accessors No Yes No Yes[6] No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No No No No No No No No Yes Yes Yes Yes
§Proxy internal calls, getter/setter methods 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 2/4 4/4 4/4 2/4 2/4 2/4 2/4 2/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 0/4 0/4 2/4 2/4 2/4 2/4 2/4 4/4 4/4 4/4 4/4 0/4 0/4 4/4 4/4 4/4 4/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 2/4 2/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 4/4 4/4
§__defineGetter__ No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No No No Yes Yes No No No No No No No No No No No Yes Yes
§__defineSetter__ No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No No No Yes Yes No No No No No No No No No No No Yes Yes
§__lookupGetter__ No No No No No No No No No No Yes Yes No No No No No Yes Yes Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No No No No No No No No No No No No No No No No Yes Yes
§__lookupSetter__ No No No No No No No No No No Yes Yes No No No No No Yes Yes Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes No No Yes Yes Yes Yes No No No No No No No No No No No No No No No No No No No No No Yes Yes
§assignments allowed in for-in head in non-strict mode MDN (Mozilla Development Network) logo  Yes No No No No No Yes Yes Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes
2018 features
§template literal revision No No No No No No No No No No No No No No No No No No No No No Yes Yes Yes No No No No No No No No No Flag Flag No No No No Yes Yes No No No No No No No No No No No No No No No No No No No No No No No

[1] Flagged features have to be enabled via "Experimental Javascript features" flag unless otherwise stated

[2] Flagged features require an optional transformer setting.

[3] Flagged features have to be enabled via "Enable experimental Javascript features" setting under about:flags

[4] Flagged features have to be enabled via --harmony or --es_staging flag

[5] The feature is enabled by default only in Firefox Nightly.

[6] This feature is supported when using TypeScript with core-js, or when a native ES6 host is used.

[7] TC39 meeting notes from July 28, 2015.

[8] 'Semantics of yield* in throw case' GitHub issue in ECMA-262 repo.

[9] TC39 meeting notes from July 29, 2015.

[10] TC39 meeting notes from July 28, 2015.

[11] TC39 meeting notes from July 28, 2015.

[12] 'Normative: Remove [[Enumerate]] and associated reflective capabilities' GitHub Pull Request in ECMA-262 repo.

[13] This feature requires native generators or regenerator-runtime, it's a part of babel-polyfill or babel-runtime.

[14] TypeScript async / await requires native generators support.

[15] The feature is enabled by default only in Firefox Developer and Firefox Nightly.

[16] The feature have to be enabled via "javascript.options.shared_memory" setting under about:config. It is enabled by default in Firefox Developer and Firefox Nightly.

[17] The feature have to be enabled via "Experimental enabled SharedArrayBuffer support in JavaScript." setting under about:flags