Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
What's this -- いまさら聞けない JavaScript の this
Search
Shuhei Kagawa
October 31, 2014
Programming
3
2k
What's this -- いまさら聞けない JavaScript の this
JavaScript の this は関数定義時に決まるのではなく、関数の呼び出し方によって変わることを解説します。
Shuhei Kagawa
October 31, 2014
Tweet
Share
More Decks by Shuhei Kagawa
See All by Shuhei Kagawa
Profiling Node.js apps on production
shuhei
0
900
Building a Pixel Art Editor with Elm
shuhei
1
790
Redux Middleware Wars (Japanese)
shuhei
8
1.9k
Redux Middleware Wars (English)
shuhei
0
180
Draw Animated Chart on React Native
shuhei
0
8.8k
Angular 2 Offline Compiler
shuhei
0
5.4k
Weird Attractors
shuhei
0
880
Angular 2 @ JS Ojisan #6-3
shuhei
1
3k
Introduction to Angular 2
shuhei
2
160
Other Decks in Programming
See All in Programming
プロダクトという一杯を作る - プロダクトチームが味の責任を持つまでの煮込み奮闘記
hiliteeternal
0
370
「次に何を学べばいいか分からない」あなたへ──若手エンジニアのための学習地図
panda_program
3
710
GUI操作LLMの最新動向: UI-TARSと関連論文紹介
kfujikawa
0
360
一人でAIプロダクトを作るならAIにはもっと働いてもらいたい / I want AI to work harder
rkaga
2
170
Vibe coding コードレビュー
kinopeee
0
400
バイブコーディングの正体——AIエージェントはソフトウェア開発を変えるか?
stakaya
5
720
階層化自動テストで開発に機動力を
ickx
1
470
Claude Code で Astro blog を Pages から Workers へ移行してみた
codehex
0
170
kiroでゲームを作ってみた
iriikeita
0
140
Scale out your Claude Code ~自社専用Agentで10xする開発プロセス~
yukukotani
2
500
PHPUnitの限界をPlaywrightで補完するテストアプローチ
yuzneri
0
370
Amazon Q CLI開発で学んだAIコーディングツールの使い方
licux
3
170
Featured
See All Featured
Principles of Awesome APIs and How to Build Them.
keavy
126
17k
Bootstrapping a Software Product
garrettdimon
PRO
307
110k
jQuery: Nuts, Bolts and Bling
dougneiner
63
7.8k
VelocityConf: Rendering Performance Case Studies
addyosmani
332
24k
Intergalactic Javascript Robots from Outer Space
tanoku
272
27k
Refactoring Trust on Your Teams (GOTO; Chicago 2020)
rmw
34
3.1k
Templates, Plugins, & Blocks: Oh My! Creating the theme that thinks of everything
marktimemedia
31
2.5k
The Straight Up "How To Draw Better" Workshop
denniskardys
235
140k
Automating Front-end Workflow
addyosmani
1370
200k
4 Signs Your Business is Dying
shpigford
184
22k
Navigating Team Friction
lara
188
15k
Writing Fast Ruby
sferik
628
62k
Transcript
What’s “this”? ͍·͞Βฉ͚ͳ͍ JavaScript ͷ this @M3 Tech Talk 2014/10/31
߳ पฏ
͜͏͍͏ίʔυʹݟ֮͑͋Γ·ͤΜ͔ʁ var header = { init: function(selector) { this.el =
$(selector); this.el.find('.show-modal').on('click', function(e) { this.showModal(); }); this.el.find('.hide-modal').on('click', function(e) { this.hideModal(); }); }, showModal: function() { /* Show modal */ }, hideModal: function() { /* Hide modal */ } }; header.init('.header');
͜ͷίʔυಈ͖·ͤΜ var header = { init: function(selector) { this.el =
$(selector); this.el.find('.show-modal').on('click', function(e) { this.showModal(); }); this.el.find('.hide-modal').on('click', function(e) { this.hideModal(); }); }, showModal: function() { /* Show modal */ }, hideModal: function() { /* Hide modal */ } }; header.init('.header');
this ʹԿ͕ೖͬͯ͘Δ͔ Ͳ͏ܾͬͯ·ΔͰ͠ΐ͏ʁ 1. this ΛแΉؔͷఆٛ࣌ͷείʔϓͰܾ·Δɻ 2. this ΛแΉؔͷఆٛͷํͰܾ·Δɻ 3.
this ΛแΉؔͷ࣮ߦ࣌ͷείʔϓͰܾ·Δɻ 4. this ΛแΉؔͷ࣮ߦͷํͰܾ·Δɻ
this ʹԿ͕ೖͬͯ͘Δ͔ Ͳ͏ܾͬͯ·ΔͰ͠ΐ͏ʁ 1. this ΛแΉؔͷఆٛ࣌ͷείʔϓͰܾ·Δɻ 2. this ΛแΉؔͷఆٛͷํͰܾ·Δɻ 3.
this ΛแΉؔͷ࣮ߦ࣌ͷείʔϓͰܾ·Δɻ 4. this ΛแΉؔͷ࣮ߦͷํͰܾ·Δɻ
this 0 ݸͷҾ • this ɺؔͷఆٛ࣌Ͱͳ͘ɺؔͷݺͼग़͠ํ ʹΑ࣮ͬͯߦ࣌ʹܾ·Δɻ
ؔݺͼग़͠ͷύλʔϯ 1. ϝιουݺͼग़͠: obj.func() 2. ؔݺͼग़͠: func() 3. ίϯετϥΫλݺͼग़͠: new
Func() 4. call, apply: func.call(obj), func.apply(obj) 5. ଞͷਓʹ࣮ߦΛͤΔ: ΠϕϯτϦεφʔͳͲ
1. ϝιουݺͼग़͠ • obj.func() ͱ͢Δͱɺthis obj ʹͳΔɻ var world
= { name: ‘World’, greet: function(greeting) { console.log(greeting + ‘, ‘ + this.name); } }; world.greet(‘Hello’); // Hello, World!
2. ؔݺͼग़͠ function greet(greeting) { console.log(greeting + ‘, ‘ +
this.name); } greet(‘Hello’); // Hello, undefined var name = ‘Window’; greet(‘Hello’); // Hello, Window • func() ͱ͢Δͱɺthis άϩʔόϧΦϒδΣΫτʢϒϥβͰ windowʣʹͳΔɻ
‘use strict’; Λ͓͏ function world() { 'use strict'; console.log('Hello, '
+ this.name); } world(); // TypeError: Cannot read property 'name' of undefined • ͨͩ͠ strict mode ͩͱ undefined ʹͳΓɺΤϥʔʹؾ ͖͍ͮ͢ɻ
3. ίϯετϥΫλݺͼग़͠ function Person(name, age) { this.name = name; this.age
= age; } var shuhei = new Person('shuhei', 32); console.log(shuhei.name, shuhei.age); // shuhei 32 • new func() ͷܗࣜͰݺͼग़͢ͱɺthis ίϯελϥΫλ ͕ฦ͢ΠϯελϯεʹͳΔɻ
4. call, apply function greet(greeting) { console.log(greeting + ', '
+ this.name); } greet.call({ name: 'call' }, ‘Hi'); // Hi, call greet.apply({ name: 'apply' }, [‘Hello']); // Hello, apply • this Λࢦఆͯؔ͠Λ࣮ߦͰ͖Δɻ • call ॱ൪ʹҾΛࢦఆ͢Δɻapply ҾΛྻͰͤΔɻ
5. ଞͷਓʹ࣮ߦΛ·͔ͤΔ var header = { init: function(selector) { this.el
= $(selector); this.el.find('.show-button').on('click', function(e) { this.showModal(); }); this.el.find('.hide-button').on('click', function(e) { this.hideModal(); }); }, showModal: function() { /* Show modal */ }, hideModal: function() { /* Hide modal */ } }; header.init('.header'); • ଞͷਓ࣍ୈɾɾɾ͓ͦΒ͘ 2 ͔ 4ɻ2ʢάϩʔόϧʣͩͱେมʂ • DOM ͷΠϕϯτϦεφʔͷ߹ɺthis ΠϕϯτΛൃՐͨ͠ DOM ཁૉɻ
ରࡦ this.el.find(‘.show-button’).on('click', this.showModal.bind(this)); this.el.find(‘.hide-button').on('click', this.hideModal.bind(this)); • มʹ this ΛೖΕ͓͍ͯͯɺมΛ͏ɻself, that,
_this ͳͲ͕Α͘ΘΕΔɻ var self = this; this.el.find('.show-button').on('click', function(e) { self.showModal(); }); this.el.find('.hide-button').on('click', function(e) { self.hideModal(); }); • Function.prototype.bind Ͱ this Λࢦఆͨؔ͠Λ࡞ΔɻIE9 Ҏ߱Ͱ͑Δ͕ PhantomJS Ͱ͑ͳ͍ͷͨΊɺCI Ͱཁҙɻes5-shim ͳͲΛೖΕΕ͑ΔΑ͏ʹͳΔɻ
·ͱΊ 1. ϝιουݺͼग़͠: obj.func() -> obj 2. ؔݺͼग़͠: func() ->
άϩʔόϧΦϒδΣΫτʢwindow) • strict mode ͳΒ undefined 3. ίϯετϥΫλݺͼग़͠: new Func() -> Πϯελϯε 4. call, apply: func.call(obj), func.apply(obj) -> obj 5. ଞͷਓʹ࣮ߦΛͤΔ: ΠϕϯτϦεφʔͳͲ -> ଞͷਓͷ࣮࣍ୈ