Actual WeakSet Use Cases
So umm... not to be annoying but I've been digging through esdiscuss and various blog posts online. I couldn't really find any use case for WeakSet (plenty of threads about naming things :P). Most material about it online fails to distinguish it from what one would use a regular Set for. All the use cases I know for WeakSet for tagging objects aren't really relevant in JS (for example - in shared
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Babel å‰æ Babelã¯å…¥åŠ›ã•ã‚ŒãŸã‚³ãƒ¼ãƒ‰ã‚’ES6 moduleã¨ã—ã¦æ‰±ã† Babel assumes that all input code is an ES6 module FAQ · Babel (çµè«–çš„ã«ã¯--blacklist strictã§ã“ã®æŒ™å‹•ã¯ç„¡åŠ¹åŒ–ã§ãã‚‹) ES6 moduleã®å‰æçŸ¥è˜ Environment Recordã¨ã„ã†ã®ã¯ãã®ã‚¹ã‚³ãƒ¼ãƒ—ã¨å¤‰æ•°ã‚’関連付ã‘ãŸã‚Šã™ã‚‹ã‚ˆã†ãªç’°å¢ƒæƒ…å ±çš„ãªã‚‚ã®ã‚’å…¥ã‚Œã‚‹å ´æ‰€ 関数ã¨ã‹ãƒ¢ã‚¸ãƒ¥ãƒ¼ãƒ«ã¨ã‹with用ã¿ãŸã„ãªä½•ç¨®é¡žã‹ã‚ã‚‹ Moduleã¯Module Environment Recordsã®ã‚’作ã£ã¦ãã“ã«æƒ…å ±ã‚’è¨˜éŒ²ã™ã‚‹ Module Environment Recordsã¯declarative Environment Recordã®ä¸€ç¨®ã§ã€åŠ ãˆã¦Module専用ã®è¨˜éŒ²é ˜åŸŸãŒã‚ã‚‹(importã®bindingã®ãŸã‚ã®å ´æ‰€) 基本的ãª
es6-iteration-protocol.md
The ECMAScript 6 iteration protocol This Gist describes my understanding of the ES6 iteration protocol (shaped by discussions I had on the es-discuss mailing list). Feedback welcome, especially w.r.t. the terminology I am introducing here (singleton iterators, closable iterators, etc.). The iteration protocol (as defined in the ECMAScript specification) comprises the following iterfaces (I have om
ECMA Script 6 Quiz
ECMAScript 6 Quiz by @mxwllt WARNING This quiz is subject to dirty tricks. Do not trust the speaker. But don't be scared to answer. var/let/const What's the output? const KEY = 'white_rabbit'; if (true) { const KEY = 'ginger_rabbit'; } console.log(KEY); white_rabbit What's the output? let x = 42; if (true) { let x = 1337; } console.log(x); 42 What's the output? let x = 42; if (true) { console.log(
new.targetメタプãƒãƒ‘ティã«ã¤ã„㦠- JS.next
æ¦‚è¦ ã€Œnew.targetã€ã¨ã¯ã€ES2015ã§å°Žå…¥ã•ã‚ŒãŸãƒ“ルトインクラスã®ã‚µãƒ–クラスを作る上ã§æ¬ ã‹ã›ãªã„å˜åœ¨ã§ã‚ã‚‹[[newTarget]]ã‚’å–å¾—ã™ã‚‹ãŸã‚ã®ãƒ¡ã‚¿ãƒ—ãƒãƒ‘ティã§ã‚る。 従æ¥ã®å•é¡Œç‚¹ ES5ã¾ã§ã¯Arrayã®ã‚ˆã†ãªãƒ“ルトインクラスをé©åˆ‡ã«ç¶™æ‰¿ã—ãŸã‚µãƒ–クラスを作るã“ã¨ãŒã§ããªã‹ã£ãŸã€‚ ES2015ã‹ã‚‰ã®ãƒ—ãƒãƒˆã‚¿ã‚¤ãƒ—è¨å®šæ©Ÿèƒ½ã‚’使ã†ã¨å¯èƒ½ã§ã‚ã‚Šã€ã“ã®ã‚ˆã†ã«ãªã‚‹ã€‚ class Stack extends Array { constructor( ...args ) { var stack = new Array( ...args ) return Object.setPrototypeOf( stack, Stack.prototype ) } clear() { this.length = 0 } } ã—ã‹ã—毎回ã“ã®ã‚ˆã†ã«æ›¸ã‹ãªã„ã¨ã„ã‘ãªã„ã®ã¯ã‚¹ãƒžãƒ¼ãƒˆã§ã¯ãªã„。 ã§ãã‚Œã°ã“ã®æ§˜ã«æ›¸
Classes (ES6) Sample
Available in Chrome 42+ | View on GitHub | Browse Samples Background ES6 Classes formalize the common JavaScript pattern of simulating class-like inheritance hierarchies using functions and prototypes. They are effectively simple sugaring over prototype-based OO, offering a convenient declarative form for class patterns which encourage interoperability. Classes (as shipped in Chrome) support proto
ECMAScript没proposal追悼å¼
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Classes in ECMAScript 6 (final semantics)
Warning: This blog post is outdated. Instead, read chapter “Classes†in “JavaScript for impatient programmersâ€. Recently, TC39 decided on the final semantics of classes in ECMAScript 6 [1]. This blog post explains how their final incarnation works. The most significant recent changes were related to how subclassing is handled. Overview  # class Point { constructor(x, y) { this.x = x; this.y = y; }
Valid JavaScript variable names in ECMAScript 6 · Mathias Bynens
ES2015 updates the grammar for identifiers. This affects a number of things, but most importantly, identifiers can be used as variable names, and identifier names are valid unquoted property names. This post describes the observable changes compared to the old ES5 behavior. Reserved words ES2015 reserves the await keyword in module contexts for use in the future. // Valid in ES5, but invalid in an
Unicode-aware regular expressions in ES2015 · Mathias Bynens
ECMAScript 2015 introduces two new flags for regular expressions: y enables ‘sticky’ matching. u enables various Unicode-related features. This article explains the effects of the u flag. It helps if you’ve read JavaScript has a Unicode problem first. Impact on syntax Setting the u flag on a regular expression enables the use of ES2015 Unicode code point escapes (\u{…}) in the pattern. // Note: `a
ユニコードエスケープシーケンスãŒæ‹¡å¼µã•ã‚ŒãŸ - JS.next
æ¦‚è¦ ä»Šã¾ã§ã¯ã‚µãƒã‚²ãƒ¼ãƒˆãƒšã‚¢ã«ã‚ˆã‚‹æ–‡å—を１シーケンスã§è¡¨ã™ã“ã¨ãŒå‡ºæ¥ãªã‹ã£ãŸãŒã€ES2015ã§ã¯ã€Ž\u{xxxxx}ã€ã®å½¢å¼ã§ã€Œ0xffffã€ã‚’超ãˆã‚‹æ–‡å—コードを表ã™ã“ã¨ãŒã§ãる。 例 var s1 = '\ud842\udf9f' var s2 = '\u{20b9f}' console.log( s1 == s2, s1, s2 ) // true "𠮟" "𠮟" 実装ã•ã‚Œã‚‹ãƒãƒ¼ã‚¸ãƒ§ãƒ³ V8　3.31.38（文å—列リテラル内）　4.2.1（æ£è¦è¡¨ç¾ãƒªãƒ†ãƒ©ãƒ«å†…）
@@toStringTagãŒå®Ÿè£…ã•ã‚ŒãŸ - JS.next
æ¦‚è¦ ä¾‹ãˆã°ã€ŽObject.prototype.toString.call([])ã€ã¨å‘¼ã¶ã¨ã€ã€Ž"[object Array]"ã€ã¨å¸°ã£ã¦ãã‚‹ãŒã€ ãã®ã€ŒArrayã€ã®éƒ¨åˆ†ã‚’ã©ã†ã„ã†è¡¨è¨˜ã«ã™ã‚‹ã‹è¨å®šã§ãるビルトインシンボルãŒå®Ÿè£…ã•ã‚ŒãŸã€‚ 例 function Cat() { } var cat = new Cat console.log( '' + cat ) // "[object Object]" Cat.prototype[Symbol.toStringTag] = 'Cat' console.log( '' + cat ) // "[object Cat]" 一部ã®ãƒ“ルドインコンストラクタã«ã¯@@toStringTagãŒå®šç¾©ã•ã‚Œã¦ã„る。 console.log( Map.prototype[Symbol.toStringTag] ) // "Map" 実装ã•ã‚Œã‚‹ãƒãƒ¼ã‚¸ãƒ§ãƒ³ V8　3
EcmaScript 6 - the future is here
Talk given at JsDay (Verona, Italy) - May 2014
イテレータã«ã¤ã„㦠- JS.next
æ¦‚è¦ V8ã§ES2015ã®ã‚¤ãƒ†ãƒ¬ãƒ¼ã‚·ãƒ§ãƒ³å‘¨ã‚Šã®å®Ÿè£…ãŒé€²ã‚“ã§ããŸã®ã§ã€è§£èª¬ã—ã¦ã¿ã‚ˆã†ã¨æ€ã†ã€‚ イテレーションã¨ã¯ ã“ã“ã§ã¯ãƒ‡ãƒ¼ã‚¿ã®è¦ç´ ã‚’ç¹°ã‚Šè¿”ã—ã¦å–り出ã™ã“ã¨ã€‚ 例ãˆã°é…列ã®forEachメソッドã¯ã€è¦ç´ やインデックスをイテレートã™ã‚‹ã‚¤ãƒ†ãƒ¬ãƒ¼ã‚¿ã§ã‚る。 ãŸã ã—ã“れらã¯ï¼ˆå†…部的ã«ï¼‰ç¹°ã‚Šè¿”ã—ã¾ã§è¡Œã†ã‚¤ãƒ†ãƒ¬ãƒ¼ã‚¿ï¼ˆå†…部イテレータ）ã ãŒã€ES2015ã§ã¯å¤–部イテレーションã®ãŸã‚ã®ä»•çµ„ã¿ãŒå…¥ã£ãŸã€‚ イテレータオブジェクト イテレータオブジェクトã¯ã€Žæ¬¡ã®è¦ç´ ã€ã‚’è¿”ã™ãƒ¡ã‚½ãƒƒãƒ‰ã‚’å‚™ãˆã¦ã„るオブジェクトã§ã‚る。 ã¤ã¾ã‚Šã‚¤ãƒ†ãƒ¬ãƒ¼ã‚·ãƒ§ãƒ³ã®ã€Žæ¬¡ã®è¦ç´ ã‚’å–り出ã™ã€ã“ã¨ã ã‘ã‚’æ‹…ã„ã€ãれを繰り返ã™ã“ã¨ã¯å¤–ã§è¡Œã‚れる（外部イテレータ）。 例 Array.prototype.values()ã¯é…列ã®è¦ç´ ã‚’é †ç•ªã«åˆ—挙ã™ã‚‹ã‚¤ãƒ†ãƒ¬ãƒ¼ã‚¿ã‚ªãƒ–ジェクトを返ã™ã€‚ var ary = [5, 4, 3] var iter = ary.valu
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1258163 - Implement Array.prototype[@@unscopables]
1135377 - Support /u flag and the relevant semantics on regular expressions
Destructuring assignmentã®ã”利用ã¯è¨ˆç”»çš„ã« - Qiita
1059908 - Method definitions and getter/setter functions should not be constructors
https://bugs.chromium.org/p/v8/issues/detail?id=3886
d21fd15467e16f185e511dbfbaeef7caddfe804a - v8/v8 - Git at Google
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