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 6 +
core-js
Babel 7 +
core-js
Closure 2018.02 Closure 2018.03 Closure 2018.04 Closure 2018.05 Closure 2018.06 Closure 2018.07 Closure 2018.08 Closure 2018.09 Closure 2018.10 Type-
Script +
core-js
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core-js
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core-js
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core-js
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es7-shim IE 10 IE 11 Edge 15 Edge 16 Edge 17 Edge 18 Edge 19 Preview FF 52 ESR FF 56 FF 57 FF 58 FF 59 FF 60 ESR FF 61 FF 62 FF 63 FF 64 Beta FF 65 Nightly OP 12.10 CH 62,
OP 49
CH 63,
OP 50
CH 64,
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CH 66,
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CH 67,
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CH 71,
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SF 10 SF 10.1 SF 11 SF 11.1 SF 12 SF TP WK PJS Node 0.10[1] Node 0.12[2] Node 4[2] Node >=6.5 <7[2] Node 7.0-7.5[2] Node >=7.6 <8[2] Node >=8.0 <8.3[2] Node >=8.3 <8.7[2] Node >=8.7 <8.10[2] Node >=8.10 <9[2] DUK 2.0 DUK 2.1 DUK 2.2 GraalVM 1.0[3] AN 4.4 AN 4.4.3 iOS 10.0-10.2 iOS >=10.3 <11 iOS 11 iOS 11.3 iOS 12
2016 features
§exponentiation (**) operator MDN (Mozilla Development Network) logo  2/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 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 0/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 0/3 3/3 3/3 3/3 3/3 3/3 3/3 0/3 0/3 0/3 0/3 0/3 3/3 3/3 3/3 3/3 3/3 3/3 2/3 2/3 2/3 3/3 0/3 0/3 0/3 3/3 3/3 3/3 3/3
§basic support 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No Flag[4] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes
§assignment 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No Flag[4] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes
§early syntax error for unary negation without parens No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No Flag[4] Yes Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§Array.prototype.includes MDN (Mozilla Development Network) logo  0/3 3/3 3/3 1/3 1/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 2/3 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 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 0/3 0/3 0/3 0/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 0/3 0/3 0/3 3/3 0/3 0/3 3/3 3/3 3/3 3/3 3/3
§Array.prototype.includes MDN (Mozilla Development Network) logo  No Yes[5] Yes[5] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§Array.prototype.includes is generic No Yes[5] Yes[5] No No Yes Yes Yes Yes Yes Yes Yes Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§%TypedArray%.prototype.includes MDN (Mozilla Development Network) logo  No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] No No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes No No No Yes No No Yes Yes 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 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§generator throw() caught by inner generator MDN (Mozilla Development Network) logo [8] No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] No No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Flag Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§strict fn w/ non-strict non-simple params is error[10] No No No No No 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§nested rest destructuring, declarations MDN (Mozilla Development Network) logo [11] No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§nested rest destructuring, parameters[12] No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§Proxy, "enumerate" handler removed MDN (Mozilla Development Network) logo [13] No No No No No 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes
§Proxy internal calls, Array.prototype.includes No No No No No 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
2017 features
§Object static methods 0/4 4/4 4/4 3/4 3/4 3/4 3/4 3/4 3/4 3/4 3/4 3/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 3/4 0/4 0/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 0/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 1/4 4/4 4/4 4/4 4/4 4/4 4/4 0/4 0/4 0/4 0/4 0/4 4/4 4/4 4/4 4/4 4/4 4/4 0/4 0/4 0/4 4/4 0/4 0/4 1/4 4/4 4/4 4/4 4/4
§Object.values MDN (Mozilla Development Network) logo  No Yes[5] Yes[5] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No Flag[4] Yes Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§Object.entries MDN (Mozilla Development Network) logo  No Yes[5] Yes[5] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No Flag[4] Yes Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§Object.getOwnPropertyDescriptors MDN (Mozilla Development Network) logo  No Yes[5] Yes[5] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No Flag[4] Yes Yes Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§Object.getOwnPropertyDescriptors doesn't provide undefined descriptors No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] No No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No Yes Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§String padding 0/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 0/2 0/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 0/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 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 0/2 2/2 2/2 2/2 2/2 0/2 0/2 0/2 2/2 0/2 0/2 2/2 2/2 2/2 2/2 2/2
§String.prototype.padStart MDN (Mozilla Development Network) logo  No Yes[5] Yes[5] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No Flag[4] Flag[4] Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§String.prototype.padEnd MDN (Mozilla Development Network) logo  No Yes[5] Yes[5] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No Flag[4] Flag[4] Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§trailing commas in function syntax MDN (Mozilla Development Network) logo  0/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 0/2 2/2 2/2 2/2 2/2 2/2 2/2 0/2 0/2 0/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 0/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 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 0/2 2/2 2/2 2/2 2/2 0/2 0/2 0/2 2/2 0/2 0/2 2/2 2/2 2/2 2/2 2/2
§in parameter lists MDN (Mozilla Development Network) logo  No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§in argument lists MDN (Mozilla Development Network) logo  No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§async functions MDN (Mozilla Development Network) logo  3/15 3/15 3/15 9/15 9/15 9/15 9/15 9/15 9/15 9/15 9/15 9/15 8/15 8/15 8/15 8/15 8/15 8/15 8/15 0/15 0/15 0/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 0/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 15/15 0/15 15/15 15/15 15/15 15/15 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 13/15 0/15 0/15 0/15 15/15 15/15 15/15 15/15
§return Yes Yes[14] Yes[14] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] No No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No Flag[4] Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§throw ? ? ? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] No No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§no line break between async and function ? ? ? 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§no "prototype" property ? ? ? No No 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§await MDN (Mozilla Development Network) logo  Yes Yes[14] Yes[14] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] No No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No Flag[4] Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes
§await, rejection ? ? ? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] No No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes
§must await a value ? ? ? Yes Yes Yes Yes Yes Yes Yes Yes Yes ? ? ? ? ? ? ? No No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§can await non-Promise values ? ? ? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] No No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§cannot await in parameters ? ? ? 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§async methods, object literals ? ? ? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] No No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§async methods, classes ? ? ? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] No No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§async arrow functions Yes Yes[14] Yes[14] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] Yes[9] No No No 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 Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No Flag[4] Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§correct prototype chain ? ? ? No No 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§async function prototype, Symbol.toStringTag ? ? ? No No 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
§async function constructor ? ? ? No No 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No ? Yes Yes Yes Yes Yes No No No Yes No No No Yes Yes 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 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 17/17 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 17/17 17/17 17/17 17/17 17/17 0/17 16/17 12/17 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 17/17 17/17 0/17 0/17 0/17 17/17 0/17 0/17 0/17 16/17 12/17 0/17 0/17
§SharedArrayBuffer 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes No[20] No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes No[20] No[20] No[20]
§SharedArrayBuffer[Symbol.species] No No No No No No No No No No No No No No No No No No No No No No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes No[20] No[20] No[20] No[20] No[20] No No No No No No No No Yes Yes Yes No No No Yes No No No Yes No[20] No[20] No[20]
§SharedArrayBuffer.prototype.byteLength 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No No No[20] No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No No No[20] No[20] No[20]
§SharedArrayBuffer.prototype.slice 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes No[20] No[20] No[20] No[20] No[20] No No No No No No No No Yes Yes Yes No No No Yes No No No Yes No[20] No[20] No[20]
§SharedArrayBuffer.prototype[Symbol.toStringTag] No No No No No No No No No No No No No No No No No No No No No No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes No[20] No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes No[20] No[20] No[20]
§Atomics.add 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
§Atomics.and 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
§Atomics.compareExchange 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
§Atomics.exchange 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
§Atomics.wait 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
§Atomics.wake 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
§Atomics.isLockFree 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
§Atomics.load 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
§Atomics.or 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
§Atomics.store 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
§Atomics.sub 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
§Atomics.xor 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 No Flag[15] Yes No[16] No[16] No[16] No[17] Yes No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No[18] No Yes No[19] No[19] No[19] No[19] No[19] Yes Yes Yes Yes Yes No Yes Yes No[20] No[20] No[20] No[20] No No No No Flag[21] Flag[21] Flag[21] Flag[21] Yes Yes Yes No No No Yes No No No Yes Yes No[20] No[20]
2017 misc
§Proxy "ownKeys" handler, duplicate keys for non-extensible targets (ES 2017 semantics) MDN (Mozilla Development Network) logo [22] No No No No No No No No No No No No No No No No No No No No No No No Yes Yes Yes Yes Yes Yes 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 Yes No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes 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 No No No No No No No No Yes Yes Yes Yes Yes Yes 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 No No No No No No Yes Yes Yes No No No Yes No No Yes Yes 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 No No No No Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes No No No Yes No No No Yes Yes Yes Yes
2017 annex b
§Object.prototype getter/setter methods 0/16 16/16 16/16 0/16 0/16 0/16 0/16 0/16 0/16 0/16 0/16 0/16 16/16 16/16 16/16 16/16 16/16 16/16 16/16 0/16 0/16 8/16 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 16/16 16/16 16/16 12/16 16/16 16/16 16/16 16/16 16/16 16/16 16/16 16/16 16/16 16/16 16/16 16/16 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 12/16 12/16 12/16 16/16 0/16 0/16 16/16 16/16 6/16 6/16 16/16 16/16 16/16 16/16 16/16
§__defineGetter__ MDN (Mozilla Development Network) logo  No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__defineGetter__, symbols No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] No No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Flag[4] Flag[4] Yes Yes Yes Yes Yes
§__defineGetter__, ToObject(this) No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No Flag[23] Flag[23] Yes No No Yes Yes No No Yes Yes Yes Yes Yes
§__defineSetter__ MDN (Mozilla Development Network) logo  No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__defineSetter__, symbols No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] No No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Flag[4] Flag[4] Yes Yes Yes Yes Yes
§__defineSetter__, ToObject(this) No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No Flag[23] Flag[23] Yes No No Yes Yes No No Yes Yes Yes Yes Yes
§__lookupGetter__ MDN (Mozilla Development Network) logo  No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__lookupGetter__, prototype chain No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__lookupGetter__, symbols No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] No No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Flag[4] Flag[4] Yes Yes Yes Yes Yes
§__lookupGetter__, ToObject(this) No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes No No No No No No No Flag[23] Flag[23] Yes No No Yes Yes No No Yes Yes Yes Yes Yes
§__lookupGetter__, data properties can shadow accessors No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes No No Yes Yes No No Yes Yes Yes Yes Yes
§__lookupSetter__ MDN (Mozilla Development Network) logo  No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__lookupSetter__, prototype chain No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes
§__lookupSetter__, symbols No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] No No No 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 Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Flag[4] Flag[4] Yes Yes Yes Yes Yes
§__lookupSetter__, ToObject(this) No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes No No No No No No No Flag[23] Flag[23] Yes No No Yes Yes No No Yes Yes Yes Yes Yes
§__lookupSetter__, data properties can shadow accessors No Yes[5] Yes[5] No No No No No No No No No Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] 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 Yes Yes Yes Yes Yes No No No No No No Yes Yes Yes Yes No No Yes 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 0/4 0/4 0/4 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 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 0/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 4/4 0/4 0/4 0/4 0/4 0/4 2/4 2/4 4/4 4/4 4/4 4/4 0/4 0/4 0/4 4/4 0/4 0/4 4/4 4/4 4/4 4/4 4/4
§__defineGetter__ No No No No No 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No Yes Yes Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§__defineSetter__ No No No No No 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No Yes Yes Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§__lookupGetter__ No No No No No 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§__lookupSetter__ No No No No No 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 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No Yes Yes Yes Yes No No No Yes No No Yes Yes Yes Yes Yes
§assignments allowed in for-in head in non-strict mode MDN (Mozilla Development Network) logo  Yes No No 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 Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes
2018 features
§object rest/spread properties 0/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 0/2 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 0/2 0/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 0/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 0/2 0/2 0/2 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 0/2 2/2 0/2 0/2 0/2 0/2 0/2 2/2 2/2
§object rest properties No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes 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[4] Yes Yes Yes No No No Yes No No No No No Yes Yes
§object spread properties No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes 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[4] Yes Yes Yes No No No Yes No No No No No Yes Yes
§Promise.prototype.finally MDN (Mozilla Development Network) logo  0/3 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 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 0/3 0/3 0/3 3/3 3/3 3/3 3/3 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 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 0/3 0/3 0/3 0/3 0/3 0/3 3/3 0/3 0/3 0/3 0/3 0/3 3/3 3/3
§basic support No Yes[5] Yes[5] No No Yes Yes Yes Yes Yes Yes Yes Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] No No No No No No Yes Yes No No No Yes Yes Yes Yes Yes Yes Yes Yes No No[24] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No No No[24] No[24] No No No Yes No No No No No Yes Yes
§don't change resolution value No Yes[5] Yes[5] No No Yes Yes Yes Yes Yes Yes Yes Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] No No No No No No Yes Yes No No No Yes Yes Yes Yes Yes Yes Yes Yes No No[24] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No No No[24] No[24] No No No Yes No No No No No Yes Yes
§change rejection value No Yes[5] Yes[5] No No Yes Yes Yes Yes Yes Yes Yes Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] Yes[6] No No No No No No Yes Yes No No No Yes Yes Yes Yes Yes Yes Yes Yes No No[24] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No No No[24] No[24] No No No Yes No No No No No Yes Yes
§s (dotAll) flag for regular expressions ? 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 No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No ? ? ? ? ? ? ? Flag[23] Flag[23] Yes ? ? No Yes ? ? No No No Yes Yes
§RegExp named capture groups 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 No No No No No No No No No No No No No Flag[23] Flag[23] Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No Flag[23] Flag[23] Flag[23] No No No Yes No No No No No Yes Yes
§RegExp Lookbehind Assertions No No No No No No No No No No No No No No No No No No No No No No 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 No No No No No No No No No No No Flag[23] Flag[23] Flag[23] Flag[23] Flag[23] Flag[23] Yes No No No Yes No No No No No No No
§RegExp Unicode Property Escapes 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 No No No No No No No No No No No No No Flag[23] Flag[23] Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No No No No No No No Flag[23] Flag[23] Flag[23] No No No Yes No No No No No Yes Yes
§Asynchronous Iterators 0/2 2/2 2/2 0/2 0/2 0/2 0/2 0/2 0/2 1/2 2/2 2/2 0/2 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 0/2 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 2/2 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 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 2/2 0/2 0/2 0/2 0/2 0/2 0/2 2/2
§async generators No Yes Yes No No No No No No Yes Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No No No No No No[25] Yes Yes Yes Yes Yes Yes Yes Yes Yes No Flag[23] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes No No No No No No No No No No Flag[23] No No No Yes No No No No No No Yes
§for-await-of loops No Yes Yes No No No No No No No Yes Yes No Yes Yes Yes Yes Yes Yes No No No No No No No No No No[25] Yes Yes Yes Yes Yes Yes Yes Yes Yes No Flag[23] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes No No No No No No No No No No Flag[23] No No No Yes No No No No No No Yes
2018 misc
§template literal revision No No No No No No No No No No No Yes 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 No 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 No Flag[23] Flag[23] Yes No No No Yes No No No No Yes Yes Yes
2019 misc
§optional catch binding 0/3 0/3 3/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 3/3 3/3 3/3 3/3 3/3 3/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 3/3 0/3 0/3 0/3 0/3 0/3 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 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 3/3 3/3
§basic No No Yes No No No No No No No No No No Yes Yes Yes Yes Yes Yes No No No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes No No No No Flag[23] Yes Yes Yes Yes Yes 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 No No No No Yes Yes
§await No No Yes No No No No No No No No No No Yes Yes Yes Yes Yes Yes No No No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes No No No No Flag[23] Yes Yes Yes Yes Yes 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 No No No No Yes Yes
§yield No No Yes No No No No No No No No No No Yes Yes Yes Yes Yes Yes No No No No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes No No No No Flag[23] Yes Yes Yes Yes Yes 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 No No No No Yes Yes

[1] Flagged features have to be enabled via --harmony flag

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

[3] Executed in Node.js/JVM mode via graalvm/bin/node --jvm.

[4] The feature have to be enabled via "Experimental Javascript features" setting under about:flags

[5] This feature is supported when using Babel with core-js.

[6] This feature is supported when using TypeScript with core-js.

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

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

[9] Requires the downlevelIteration compile option.

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

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

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

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

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

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

[16] The feature was temporarily disabled to mitigate the Meltdown and Spectre CPU bugs.

[17] The feature is available only in Firefox Developer Edition and Firefox Nightly builds.

[18] The feature was temporarily disabled to mitigate the Meltdown and Spectre CPU bugs.

[19] The feature was temporarily disabled to mitigate the Meltdown and Spectre CPU bugs.

[20] The feature was temporarily disabled to mitigate the Meltdown and Spectre CPU bugs.

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

[22] The behaviour of the Proxy “ownKeys” handler in presence of duplicate keys has been modified later.

[23] The feature have to be enabled via --js-flags="--harmony" flag

[24] The feature is considered unstable, but can be enabled via --js-flags="--harmony-promise-finally" flag

[25] The feature is available only in Firefox Nightly builds.