ECMAScriptの視点で見る WeakRefの“正しい”使い方

Ginza.js#7のLTです。

1. &$."4DSJQUך鋔挿ד鋅׷ 8FBL3FGךˑ姻׃ְ˒⢪ְ倯 (JO[BKT
   
   
   
   !VIZP@
2. 荈䊹稱➜ –ؿٗٝزؒٝسؒٝآص،!-*/&吳䒭⠓爡 – +BWB4DSJQU娖䎃ֻ׵ְ –2JJUB蔓➂&$."4DSJQUةؚDPOUSJCVUJPO侧⡘ – չ+BWB4DSJQUך \
   ^
   ׾椚鍑ׅ׷պ – չ➙ַ׵ד׮鷄ְאֽ׷ +BWB4DSJQUךչ垥彊ٓ؎ـٓٔպ׾㷕עպ – չ׉׹׉׹+BWB4DSJQUח䱰欽ׁ׸׉ֲז0QUJPOBM
   $IBJOJOH׾➙ׁ׵䗡䎿鍑铡պ זו !VIZP@
3. !VIZP@ 5BCMF
   PG
   $POUFOUT  8FBL3FGך䗁统  &$."4DSJQUהؖك٦آ؝ؙٖءّٝךꟼ⤘  8FBL3FGכ➬圫חוך״ֲח剅ַ׸׋ךַ  8FBL3FGָ䧮ղח♷ִ׷⥂鏾כ⡦ַ
4. !VIZP@ 8FBL3FGך䗁统 –4UBHF
   فٗه٦ؠٕ –8FBL3FG
   ؔـآؙؑزפך䓲⿫撑׾⡲䧭דֹ׷װא –'JOBMJ[BUJPO(SPVQ
   ؔـآؙؑزָؖك٦آ؝ؙٖز ׁ׸׋׵؝٦ٕغحؙㄎ׿דֻ׸׷װא ˟DG
   8FBL3FG
   +BWB4DSJQUח䓲⿫撑ָװ׏גֻ׷אְדח'JOBMJ[BUJPO׮  2JJUB 㹑⠗
5. !VIZP@ 8FBL3FGך⢽ const ref = new WeakRef(new ArrayBuffer(1024 ** 3)); console.log(ref.deref()); // ArrayBuffer setTimeout(()=> { gc(); console.log(ref.deref()); // undefined }, 100); new WeakRef ⦼ ד⦼פך䓲⿫撑׾⡲䧭 䓲⿫撑ך⚥魦כderef ًاحسד铣׬ ($ח״׏ג䓲⿫撑ָ ⥂䭯ׅ׷ؔـآؙؑز ָ嶊ִ׋
6. !VIZP@ 8FBL3FGך⢽嶊ִזְ㜥さ const buf = new ArrayBuffer(1024 ** 3); const ref = new WeakRef(buf); console.log(ref.deref()); // ArrayBuffer console.log(ref.deref() === buf); // true setTimeout(()=> { gc(); console.log(ref.deref()); // ArrayBuffer console.log(buf.byteLength); // 1073741824 }, 100); 㢌侧CVGח⦼׾Ⰵ׸׋ 䓲ֻזְ⿫撑 䓲⿫撑ך⚥魦כ 床׃׋⦼הずׄ ($䖓׮嶊ִגְזְ 㢌侧buf׾鸐ׄג⦼ח ،ؙإأ〳腉זךד
7. !VIZP@ 'JOBMJ[BUJPO(SPVQך⢽ const group = new FinalizationGroup( iterator => console.log([...iterator])); let obj = new ArrayBuffer(1024 ** 3); group.register(obj, 'דְַر٦ة’); obj = null; gc(); // [‘דְַر٦ة’] ה邌爙ׁ׸׷ ؔـآؙؑزָ($ׁ׸׋ הֹחㄎעꟼ侧׾床ׅ 'JOBMJ[BUJPO(SPVQך 湊鋔㼎韋ח obj׾鷄⸇ objפך⿫撑׾嶊ׅ objָ($〳腉חז׷ objָ($ׁ׸ג؝٦ٕ غحָؙㄎל׸׷
8. &$."4DSJQUה($
9. !VIZP@ &$."4DSJQUה($ 2
   הֿ׹דծ+4ך鎉铂➬圫&$."4DSJQUדכ ($כֿ׸תדוֲ䪔׻׸גְ׋ך ˟
   &$."4DSJQU +BWB4DSJQUך鎉铂➬圫׾㹀׭׷㕂ꥷ鋉呓կ չ+BWB4DSJQUպהչ&$."4DSJQUպך麩ְחכ长铡֮׷ָծ娖〷涸穗箮דせ⵸ָ麩ֲ׌ֽד䊴殯כ זְהְֲךָ涪邌罏ך䭯锷կ
10. !VIZP@ &$."4DSJQUה($ 2
    הֿ׹דծ+4ך鎉铂➬圫&$."4DSJQUדכ ($כֿ׸תדוֲ䪔׻׸גְ׋ך " ⡦׮㹀纏ׁ׸גְתׇ׿ד׃׋ ˟
    8FBL.BQך眍ח׍׳׏ה׌ֽ($פך鎉⿹ָ֮׷ָ/05&玎䏝 ˟
    &$."4DSJQU +BWB4DSJQUך鎉铂➬圫׾㹀׭׷㕂ꥷ鋉呓կ չ+BWB4DSJQUպהչ&$."4DSJQUպך麩ְחכ长铡֮׷ָծ娖〷涸穗箮דせ⵸ָ麩ֲ׌ֽד䊴殯כ זְהְֲךָ涪邌罏ך䭯锷կ
11. !VIZP@ &$."4DSJQUה($ 2
    ז׈⡦׮㹀纏ׁ׸גְזַ׏׋ך " ($כفؚٗٓيך䮙⹛חⰋֻ䕦갟׾⿹רׁזְַ׵ –($כⳢ椚禸ח״׷剑黝⻉חֺׅזְ湡涸ًٌٔ⢪欽ꆀ׾⵴幾 –剑黝⻉דفؚٗٓيך䮙⹛ָ㢌׻׷ץֹדכזְ ˟
    ($ָ䮠ת׷ְׇדفؚٗٓيךػؿؓ٦وٝأָ衅׍׋׶ׅ׷ַ׮׃׸זְָծ ػؿؓ٦وٝأכ鎉铂➬圫ד⥂鏾ׁ׸גְזְךד➙㔐כ莆㄂ז׃
12. !VIZP@ 8FBL3FGך&$."4DSJQUפך䕦갟 2
    ד׮8FBL3FGכفؚٗٓيך䮙⹛ח䕦갟ׅ׷״י
13. !VIZP@ 8FBL3FGך&$."4DSJQUפך䕦갟 2
    ד׮8FBL3FGכفؚٗٓيך䮙⹛ח䕦갟ׅ׷״י " ׉ֲדׅי אְח&$."4DSJQUחؖك٦آ؝ؙٖءّٝך嚊䙀ָ
14. !VIZP@ 8FBL3FG➬圫ח鋅׷($ IUUQTUDFTQSPQPTBMXFBLSFGT ״׶䒷欽
15. !VIZP@ 8FBL3FG➬圫ח鋅׷($ ˑֿך➬圫כؖك٦آ؝ؙٖءّٝח㼎׃ג⡦׵ך⥂鏾׮遤׻זְ˒ IUUQTUDFTQSPQPTBMXFBLSFGT ״׶䒷欽
16. !VIZP@ ؖك٦آ؝ؙٖءّٝך➬圫♳ך㹀纏 Ⳣ椚禸כ⟣䠐ךة؎ىؚٝדˑMJWFדזְ˒ؔـآؙؑز׾8FBL3FGַ׵ 嶊׃ג׮葺ְ⥂鏾כ搀ְ宕黅ח嶊ׁ׸זְ〳腉䚍׮֮׷ • ˑMJWFדזְ˒ؔـآؙؑزؖك٦آ؝ؙٖءّٝך㼎韋ח ז׶䖤׷ؔـآؙؑزך䬄韋涸ז邌植
17. !VIZP@ MJWFזؔـآؙؑزך㹀纏 㼛勻涸ח8FBL3FG⟃㢩ך䩛媮דفؚٗٓيַ׵錁庠 
     ׁ׸׷ֿה ךזְؔـآؙؑز
18. !VIZP@ MJWFזؔـآؙؑزך㹀纏 㼛勻涸ח8FBL3FG⟃㢩ך䩛媮דفؚٗٓيַ׵錁庠 
     ׁ׸׷ֿה ךזְؔـآؙؑز 錁庠הכ!!!!!!!!!! ˟׮׏ה׍ׯ׿ה׃׋㹀纏ח׃״ֲהְֲ陽锷כ֮׶תׅ
19. תה׭
20. !VIZP@ ➬圫חֶֽ׷8FBL3FGך⥂鏾 –($ָ饯ֿ׷⥂鏾כ搀ְⳢ椚禸⣛㶷 –($㼎韋הז׷ؔـآؙؑزך⿑㺘ז㹀纏׮Ⳣ椚禸⣛㶷 –׬׃׹8FBL3FGכ⥂鏾׾幾׵ׅ չفؚٗٓيָ⥂䭯ׅ׷ؔـآؙؑزכ($ׁ׸זְպהְֲ⥂鏾׾PQU
    PVU〳腉
21. !VIZP@ 8FBL3FGך䠐纏 8FBL3FGכ⥂鏾׾幾׵ׅ Ⳣ椚禸ךⵖ秈ָ幾׷ 剑黝⻉ך堣⠓ָ㟓⸇ Ⱗ⡤涸חכًٌٔך⢪欽ꆀ⵴幾
22. !VIZP@ תה׭ 8FBL3FGכ剑黝⻉ָ׉ך㈓♧ך㶷㖈䠐纏ד֮׶ծ ➭ך湡涸ד⢪ֲךכ⡦ַָ呎劤涸חֶַ׃ְךד 罋ִ湫׃ת׃׳ֲ 'JOBMJ[BUJPO(SPVQ׮ず圫