V8 SpiderMonkey JavaScriptCore Chakra Other
Minor difference (1 point) Small feature (2 points) Medium feature (4 points) Large feature (8 points)
Compilers/polyfills Desktop browsers Servers/runtimes Mobile
Feature name Current browser Traceur Babel +
core-js
[2]
Closure Type-
Script +
core-js
es7-shim IE 10 IE 11 Edge 12 Edge 13 Edge 14 Edge 15 Edge 16 Preview FF 45 ESR FF 47 FF 48 FF 49 FF 50 FF 51 FF 52 ESR FF 53 FF 54 FF 55 Beta FF 56 Nightly 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
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CH 57,
OP 44
[1]
CH 58,
OP 45
[1]
CH 59,
OP 46
[1]
CH 60,
OP 47
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CH 61,
OP 48
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SF 8 SF 9 SF 10 SF 10.1 SF 11 SF TP WK PJS Node 0.10[3] Node 0.12[3] io.js[3] Node 4[3] Node 5[3] Node 6.0-6.4[3] Node >=6.5 <7[3] Node 7.0-7.5[3] Node >=7.6 <8[3] Node 8[3] DUK 2.0 DUK 2.1 iOS 8 iOS 9 iOS 10.0-10.2 iOS >=10.3 <11 iOS 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 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 3/3 0/3 3/3 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 3/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 3/3 3/3 3/3 2/3 2/3 0/3 0/3 0/3 3/3 3/3
§basic support Yes Yes Yes Yes No No No No Flag[4] Yes Yes Yes No[5] No[5] No[5] No[5] No[5] No[5] Yes Yes Yes Yes Yes Flag Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No Flag Yes Yes Yes Yes Yes No No No Yes Yes
§assignment Yes Yes Yes Yes No No No No Flag[4] Yes Yes Yes No No No[5] No[5] No[5] No[5] Yes Yes Yes Yes Yes Flag Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No Flag Yes Yes Yes Yes Yes No No No Yes Yes
§early syntax error for unary negation without parens No Yes Yes No No No No No No Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes Flag Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No Flag Yes Yes Yes No No No No No Yes 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 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 3/3 3/3 3/3 0/3 2/3 3/3 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 3/3 0/3 0/3 0/3 2/3 3/3 3/3 3/3
§Array.prototype.includes MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes 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 Yes Yes Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes
§Array.prototype.includes is generic No Yes No Yes[6] Yes 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 Yes Yes Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes
§%TypedArray%.prototype.includes MDN (Mozilla Development Network) logo  No Yes No Yes[6] 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 Yes No No No No No No Yes Yes Yes Yes Yes No No No No Yes 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 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 No Yes Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes No No No No Yes Yes Yes
§generator throw() caught by inner generator MDN (Mozilla Development Network) logo [8] No No Yes 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 Yes No No Flag Flag Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes
§strict fn w/ non-strict non-simple params is error[9] No No No No No No No Yes Yes Yes Yes Yes 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 Yes No No No No No No Yes Yes Yes Yes Yes No No No No Yes Yes Yes
§nested rest destructuring, declarations MDN (Mozilla Development Network) logo [10] No Yes Yes Yes No No No No Flag[4] 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 No No No Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes No No No No No Yes Yes
§nested rest destructuring, parameters[11] No Yes Yes Yes No No No No Flag[4] 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 No No No Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes No No No No No Yes Yes
§Proxy, "enumerate" handler removed MDN (Mozilla Development Network) logo [12] 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 No No Yes Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes
§Proxy internal calls, Array.prototype.includes No No 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 Yes No No No No No No Yes Yes Yes Yes Yes No No No No Yes 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 2/4 4/4 4/4 0/4 2/4 2/4 2/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 0/4 0/4 0/4 4/4 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 4/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 0/4 4/4 4/4 4/4 0/4 0/4 0/4 0/4 1/4 4/4 4/4
§Object.values MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes No No No No Yes Yes Yes No[5] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Flag Flag Flag Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No Flag Yes Yes Yes No No No No No Yes Yes
§Object.entries MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes No No No No Yes Yes Yes No[5] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Flag Flag Flag Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No Flag Yes Yes Yes No No No No No Yes Yes
§Object.getOwnPropertyDescriptors MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes No No No No No Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes Flag Flag Flag Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No Flag Yes Yes Yes No No No No Yes Yes Yes
§Object.getOwnPropertyDescriptors doesn't provide undefined descriptors No No No No No No No No No No Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No Yes Yes Yes No No No No No Yes Yes
§String padding 0/2 2/2 0/2 2/2 2/2 0/2 0/2 0/2 0/2 0/2 2/2 2/2 0/2 0/2 2/2 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 2/2 2/2 2/2 2/2 2/2 0/2 0/2 2/2 2/2 2/2 2/2 2/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 0/2 2/2 0/2 0/2 0/2 0/2 2/2 2/2 2/2
§String.prototype.padStart MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes No No No No Flag[4] Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No Flag Flag Flag Flag Flag Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No No Flag Flag Yes No No No No Yes Yes Yes
§String.prototype.padEnd MDN (Mozilla Development Network) logo  No Yes No Yes[6] Yes No No No No Flag[4] Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No Flag Flag Flag Flag Flag Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No No Flag Flag Yes No No No No Yes 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 2/2 2/2 2/2 0/2 0/2 0/2 0/2 0/2 0/2 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 2/2 0/2 0/2 0/2 0/2 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
§in parameter lists MDN (Mozilla Development Network) logo  No Yes No Yes No No No No No Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes No No No No No No Flag Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No No No No Yes No No No No Yes Yes Yes
§in argument lists MDN (Mozilla Development Network) logo  No Yes No Yes No No No No No Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes No No No No No No Flag Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No No No No Yes No No No No Yes 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 15/15 15/15 0/15 0/15 0/15 0/15 0/15 0/15 15/15 15/15 15/15 15/15 15/15 0/15 0/15 0/15 0/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 0/15 0/15 0/15 15/15 15/15 15/15 15/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 0/15 15/15 15/15 0/15 0/15 0/15 0/15 0/15 15/15 15/15
§return Yes Yes[13] Yes Yes[14] No No No No Flag[4] Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No Flag Flag Flag Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No Flag Yes Yes No No No No No Yes Yes
§throw ? ? ? ? No No No No Flag[4] Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes Yes
§no line break between async and function ? ? ? ? No No No No No Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes Yes
§no "prototype" property ? ? ? ? No No No No Flag[4] Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes Yes
§await MDN (Mozilla Development Network) logo  Yes Yes[13] Yes Yes[14] No No No No Flag[4] Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No Flag Flag Flag Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No Flag Yes Yes No No No No No Yes Yes
§await, rejection ? ? ? ? No No No No Flag[4] Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes Yes
§must await a value ? ? ? ? No No No No Flag[4] Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes Yes
§can await non-Promise values ? ? ? ? No No No No Flag[4] Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes Yes
§cannot await in parameters ? ? ? ? No No No No Flag[4] Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes Yes
§async methods, object literals ? ? ? ? No No No No Flag[4] Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes Yes
§async methods, classes ? ? ? ? No No No No Flag[4] Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes Yes
§async arrow functions Yes Yes[13] Yes No No No No No Flag[4] Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No Flag Flag Flag Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No Flag Yes Yes No No No No No Yes Yes
§correct prototype chain ? ? ? ? No No No No No Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes Yes
§async function prototype, Symbol.toStringTag ? ? ? ? No No No No No No Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes Yes
§async function constructor ? ? ? ? No No No No No Flag[4] Yes Yes No No No No No No Yes Yes Yes Yes Yes No ? ? ? Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No ? Yes Yes No No No No No Yes 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 17/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 17/17 17/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 0/17 17/17 17/17 0/17 0/17 0/17 16/17 17/17 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 16/17 17/17
§SharedArrayBuffer MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§SharedArrayBuffer[Symbol.species] No No No No No No No No No No Flag[4] Yes No No No No No No No[15] Flag[16] Flag[16] Yes Yes No No No No No No No No No Yes Yes No No No Yes Yes Yes Yes No No No No No No No No No No No No No No No No Yes Yes
§SharedArrayBuffer.prototype.byteLength MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No No Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No No Yes
§SharedArrayBuffer.prototype.slice MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No No No No No No[15] Flag[16] Flag[16] Yes Yes No No No No No No No No No Yes Yes No No No Yes Yes Yes Yes No No No No No No No No No No No No No No No No Yes Yes
§SharedArrayBuffer.prototype[Symbol.toStringTag] No No No No No No No No No No Flag[4] Yes No No No No No No No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.add MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.and MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.compareExchange MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.exchange MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.wait MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.wake MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.isLockFree MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.load MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.or MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.store MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.sub MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes Yes
§Atomics.xor MDN (Mozilla Development Network) logo  No No No No No No No No No No Flag[4] Yes No No[5] No[5] No[5] No[5] No[15] No[15] Flag[16] Flag[16] Yes Yes Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] Yes Yes No No No Yes Yes Yes Yes No No No No No No Flag[17] Flag[17] Flag[17] Flag[17] Flag[17] No No No No No Yes 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes Yes Yes No No Yes 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 Yes Yes Yes No No No No No No No No Yes Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No No No No No No No No No Yes 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 Yes Yes Yes Yes No No No No No Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No No No Yes No No No No No Yes Yes
2017 annex b
§Object.prototype getter/setter methods 0/16 16/16 0/16 16/16 0/16 0/16 8/16 12/16 12/16 12/16 12/16 12/16 14/16 14/16 16/16 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 12/16 12/16 12/16 12/16 12/16 12/16 16/16 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 12/16 0/16 0/16 12/16 16/16 16/16 16/16 16/16
§__defineGetter__ MDN (Mozilla Development Network) logo  No Yes No Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes
§__defineGetter__, symbols 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 No Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes
§__defineGetter__, ToObject(this) No Yes No Yes[6] No No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No Flag Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No No Yes Yes Yes Yes Yes
§__defineSetter__ MDN (Mozilla Development Network) logo  No Yes No Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes
§__defineSetter__, symbols 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 No Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes
§__defineSetter__, ToObject(this) No Yes No Yes[6] No No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No Flag Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No No Yes Yes Yes Yes Yes
§__lookupGetter__ MDN (Mozilla Development Network) logo  No Yes No Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes
§__lookupGetter__, prototype chain No Yes No Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes
§__lookupGetter__, symbols 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 No Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes
§__lookupGetter__, ToObject(this) No Yes No Yes[6] 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 Flag Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No No Yes 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 No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No Yes No No Yes Yes Yes Yes Yes
§__lookupSetter__ MDN (Mozilla Development Network) logo  No Yes No Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes
§__lookupSetter__, prototype chain No Yes No Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes
§__lookupSetter__, symbols 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 No Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes
§__lookupSetter__, ToObject(this) No Yes No Yes[6] 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 Flag Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No No No No Yes 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 No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No No Yes No No Yes 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 2/4 4/4 4/4 4/4 2/4 2/4 2/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 0/4 2/4 2/4 2/4 2/4 2/4 4/4 4/4 4/4 4/4 4/4 0/4 0/4 4/4 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 4/4 0/4 0/4 0/4 0/4 4/4 4/4 4/4
§__defineGetter__ No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No No Yes Yes Yes No No No No Yes Yes Yes
§__defineSetter__ No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No No Yes Yes Yes No No No No Yes Yes Yes
§__lookupGetter__ No No No No No No No No No Yes Yes Yes No No No Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No No No No Yes No No No No Yes Yes Yes
§__lookupSetter__ No No No No No No No No No Yes Yes Yes No No No Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No No No No Yes No No No No Yes Yes Yes
§assignments allowed in for-in head in non-strict mode MDN (Mozilla Development Network) logo  Yes No No No No Yes Yes Yes Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes 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 Yes Yes Yes Yes No No No No No No No No Flag Flag Flag No No No No Yes Yes Yes No No No No No No No No No No No No No No No No No Yes

[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 --harmony or --es_staging flag

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

[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