{
"chrome": {
"version_added": "21"
},
"chrome_android": {
"version_added": "25"
},
"edge": {
"version_added": "12"
},
"firefox": {
"version_added": "36",
"notes": [
"Prior to Firefox 13, <code>const</code> is implemented, but re-assignment is not failing.",
"Prior to Firefox 46, a <code>TypeError</code> was thrown on redeclaration instead of a <code>SyntaxError</code>."
]
},
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"version_added": "36",
"notes": [
"Prior to Firefox 13, <code>const</code> is implemented, but re-assignment is not failing.",
"Prior to Firefox 46, a <code>TypeError</code> was thrown on redeclaration instead of a <code>SyntaxError</code>."
]
},
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"version_added": "11"
},
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},
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"version_added": "9"
},
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"version_added": "10.1"
},
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"version_added": "5.1"
},
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"version_added": "6"
},
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},
"webview_android": {
"version_added": "≤37"
}
}{
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{
"version_added": "49"
},
{
"version_added": "48",
"version_removed": "49",
"flags": [
{
"type": "preference",
"name": "Enable Experimental JavaScript Features"
}
],
"notes": "Support outside of <a href='https://developer.mozilla.org/docs/Web/JavaScript/Reference/Strict_mode'>strict mode</a>."
},
{
"version_added": "41",
"version_removed": "49",
"partial_implementation": true,
"notes": "<a href='https://developer.mozilla.org/docs/Web/JavaScript/Reference/Strict_mode'>Strict mode</a> is required."
}
],
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{
"version_added": "49"
},
{
"version_added": "48",
"version_removed": "49",
"flags": [
{
"type": "preference",
"name": "Enable Experimental JavaScript Features"
}
],
"notes": "Support outside of <a href='https://developer.mozilla.org/docs/Web/JavaScript/Reference/Strict_mode'>strict mode</a>."
},
{
"version_added": "41",
"version_removed": "49",
"partial_implementation": true,
"notes": "<a href='https://developer.mozilla.org/docs/Web/JavaScript/Reference/Strict_mode'>Strict mode</a> is required."
}
],
"edge": [
{
"version_added": "14"
},
{
"version_added": "12",
"version_removed": "14",
"partial_implementation": true,
"notes": "In Edge 12 and 13, <code>let</code> within a <code>for</code> loop initializer does not create a separate variable for each loop iteration as defined by ES2015. Instead, it behaves as though the loop were wrapped in a scoping block with the <code>let</code> immediately before the loop."
}
],
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"version_added": "44",
"notes": [
"Prior to Firefox 44, <code>let</code> is only available to code blocks in HTML wrapped in a <code><script type=\"application/javascript;version=1.7\"></code> block (or higher version) and has different semantics (e.g. no temporal dead zone).",
"Prior to Firefox 46, a <code>TypeError</code> is thrown on redeclaration instead of a <code>SyntaxError</code>.",
"Firefox 54 adds support of <code>let</code> in workers."
]
},
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"version_added": "44",
"notes": [
"Prior to Firefox 44, <code>let</code> is only available to code blocks in HTML wrapped in a <code><script type=\"application/javascript;version=1.7\"></code> block (or higher version) and has different semantics (e.g. no temporal dead zone).",
"Prior to Firefox 46, a <code>TypeError</code> is thrown on redeclaration instead of a <code>SyntaxError</code>.",
"Firefox 54 adds support of <code>let</code> in workers."
]
},
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"version_added": "11",
"partial_implementation": true,
"notes": "In Internet Explorer, <code>let</code> within a <code>for</code> loop initializer does not create a separate variable for each loop iteration as defined by ES2015. Instead, it behaves as though the loop were wrapped in a scoping block with the <code>let</code> immediately before the loop."
},
"nodejs": {
"version_added": "6.0.0"
},
"opera": {
"version_added": "17"
},
"opera_android": {
"version_added": "18"
},
"safari": {
"version_added": "10"
},
"safari_ios": {
"version_added": "10"
},
"samsunginternet_android": [
{
"version_added": "5.0"
},
{
"notes": "<a href='https://developer.mozilla.org/docs/Web/JavaScript/Reference/Strict_mode'>Strict mode</a> is required.",
"partial_implementation": true,
"version_added": "4.0",
"version_removed": "5.0"
}
],
"webview_android": [
{
"version_added": "49"
},
{
"version_added": "41",
"version_removed": "49",
"partial_implementation": true,
"notes": "<a href='https://developer.mozilla.org/docs/Web/JavaScript/Reference/Strict_mode'>Strict mode</a> is required."
}
]
}{
"chrome": {
"version_added": "45"
},
"chrome_android": {
"version_added": "45"
},
"edge": {
"version_added": "12"
},
"firefox": {
"version_added": "22",
"notes": [
"The initial implementation of arrow functions in Firefox made them automatically strict. This has been changed as of Firefox 24. The use of <code>'use strict';</code> is now required.",
"Prior to Firefox 39, a line terminator (<code>\\n</code>) was incorrectly allowed after arrow function arguments. This has been fixed to conform to the ES2015 specification and code like <code>() \\n => {}</code> will now throw a <code>SyntaxError</code> in this and later versions."
]
},
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"version_added": "22",
"notes": [
"The initial implementation of arrow functions in Firefox made them automatically strict. This has been changed as of Firefox 24. The use of <code>'use strict';</code> is now required.",
"Prior to Firefox 39, a line terminator (<code>\\n</code>) was incorrectly allowed after arrow function arguments. This has been fixed to conform to the ES2015 specification and code like <code>() \\n => {}</code> will now throw a <code>SyntaxError</code> in this and later versions."
]
},
"ie": {
"version_added": false
},
"nodejs": {
"version_added": true
},
"opera": {
"version_added": "32"
},
"opera_android": {
"version_added": "32"
},
"safari": {
"version_added": "10"
},
"safari_ios": {
"version_added": "10"
},
"samsunginternet_android": {
"version_added": "5.0"
},
"webview_android": {
"version_added": "45"
}
}{
"chrome": {
"version_added": "32"
},
"chrome_android": {
"version_added": "32"
},
"edge": {
"version_added": "12"
},
"firefox": {
"version_added": "29"
},
"firefox_android": {
"version_added": "29"
},
"ie": {
"version_added": false
},
"nodejs": {
"version_added": "0.12"
},
"opera": {
"version_added": "19"
},
"opera_android": {
"version_added": "19"
},
"safari": {
"version_added": "8"
},
"safari_ios": {
"version_added": "8"
},
"samsunginternet_android": {
"version_added": "2.0"
},
"webview_android": {
"version_added": "4.4.3"
}
}{
"chrome": {
"version_added": "42"
},
"chrome_android": {
"version_added": "42"
},
"edge": {
"version_added": "14"
},
"firefox": [
{
"version_added": "39"
},
{
"version_added": "34",
"flags": [
{
"type": "preference",
"name": "dom.fetch.enable"
}
]
},
{
"version_added": "52",
"notes": "<code>fetch()</code> now defined on <code><a href='https://developer.mozilla.org/docs/Web/API/WindowOrWorkerGlobalScope'>WindowOrWorkerGlobalScope</a></code> mixin."
}
],
"firefox_android": [
{
"version_added": "39"
},
{
"version_added": "34",
"flags": [
{
"type": "preference",
"name": "dom.fetch.enable"
}
]
},
{
"version_added": "52",
"notes": "<code>fetch()</code> now defined on <code><a href='https://developer.mozilla.org/docs/Web/API/WindowOrWorkerGlobalScope'>WindowOrWorkerGlobalScope</a></code> mixin."
}
],
"ie": {
"version_added": false
},
"opera": [
{
"version_added": "29"
},
{
"version_added": "28",
"flags": [
{
"type": "preference",
"name": "Experimental Web Platform Features"
}
]
}
],
"opera_android": [
{
"version_added": "29"
},
{
"version_added": "28",
"flags": [
{
"type": "preference",
"name": "Experimental Web Platform Features"
}
]
}
],
"safari": {
"version_added": "10.1"
},
"safari_ios": {
"version_added": "10.3"
},
"samsunginternet_android": {
"version_added": "4.0"
},
"webview_android": {
"version_added": "42"
}
}{
"chrome": {
"version_added": "55"
},
"chrome_android": {
"version_added": "55"
},
"edge": {
"version_added": "15"
},
"firefox": {
"version_added": "52"
},
"firefox_android": {
"version_added": "52"
},
"ie": {
"version_added": false
},
"nodejs": [
{
"version_added": "7.6.0"
},
{
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"flags": [
{
"type": "runtime_flag",
"name": "--harmony"
}
]
}
],
"opera": {
"version_added": "42"
},
"opera_android": {
"version_added": "42"
},
"safari": {
"version_added": "10.1"
},
"safari_ios": {
"version_added": "10.3"
},
"samsunginternet_android": {
"version_added": "6.0"
},
"webview_android": {
"version_added": "55"
}
}{
"chrome": {
"version_added": "55"
},
"chrome_android": {
"version_added": "55"
},
"edge": {
"version_added": "14"
},
"firefox": {
"version_added": "52"
},
"firefox_android": {
"version_added": "52"
},
"ie": {
"version_added": false
},
"nodejs": [
{
"version_added": "7.6.0"
},
{
"version_added": "7.0.0",
"flags": [
{
"type": "runtime_flag",
"name": "--harmony"
}
]
}
],
"opera": {
"version_added": "42"
},
"opera_android": {
"version_added": "42"
},
"safari": {
"version_added": "10.1"
},
"safari_ios": {
"version_added": "10.3"
},
"samsunginternet_android": {
"version_added": "6.0"
},
"webview_android": {
"version_added": "55"
}
}{
"chrome": [
{
"version_added": "49"
},
{
"version_removed": "49",
"version_added": "42",
"notes": "Strict mode is required."
},
{
"version_removed": "49",
"version_added": "42",
"flags": [
{
"type": "preference",
"name": "Experimental JavaScript",
"value_to_set": "Enabled"
}
]
}
],
"chrome_android": [
{
"version_added": "49"
},
{
"version_removed": "49",
"version_added": "42",
"notes": "Strict mode is required."
},
{
"version_removed": "49",
"version_added": "42",
"flags": [
{
"type": "preference",
"name": "Experimental JavaScript",
"value_to_set": "Enabled"
}
]
}
],
"edge": {
"version_added": "13"
},
"firefox": {
"version_added": "45"
},
"firefox_android": {
"version_added": "45"
},
"ie": {
"version_added": false
},
"nodejs": [
{
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},
{
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"flags": [
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"type": "runtime_flag",
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{
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"flags": [
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"type": "runtime_flag",
"name": "--harmony"
}
]
}
],
"opera": [
{
"version_added": "36"
},
{
"version_removed": "36",
"version_added": "29",
"notes": "Strict mode is required."
},
{
"version_removed": "36",
"version_added": "29",
"flags": [
{
"type": "preference",
"name": "Experimental JavaScript",
"value_to_set": "Enabled"
}
]
}
],
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{
"version_added": "36"
},
{
"version_removed": "36",
"version_added": "29",
"notes": "Strict mode is required."
},
{
"version_removed": "36",
"version_added": "29",
"flags": [
{
"type": "preference",
"name": "Experimental JavaScript",
"value_to_set": "Enabled"
}
]
}
],
"safari": {
"version_added": "9"
},
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"version_added": "9"
},
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{
"version_added": "5.0"
},
{
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"version_added": "4.0",
"notes": "Strict mode is required."
}
],
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{
"version_added": "49"
},
{
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"version_added": "42",
"notes": "Strict mode is required."
}
]
}{
"chrome": {
"version_added": "74"
},
"chrome_android": {
"version_added": "74"
},
"edge": {
"version_added": "79"
},
"firefox": {
"version_added": false
},
"firefox_android": {
"version_added": false
},
"ie": {
"version_added": false
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},
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},
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"version_added": "53"
},
"safari": {
"version_added": false
},
"safari_ios": {
"version_added": false
},
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}
}