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
TypeScript で Optional Chaining を使ってみた
Search
Masaki Koyanagi
October 25, 2019
Programming
1
740
TypeScript で Optional Chaining を使ってみた
WeJS @ 37th
https://wajs.connpass.com/event/150356/
Masaki Koyanagi
October 25, 2019
Tweet
Share
More Decks by Masaki Koyanagi
See All by Masaki Koyanagi
Vitestを使った型テストの始め方
mascii
6
3k
WebHID API でリングコン のセンサー値を取得してみた
mascii
1
1.1k
Pros and Cons で考える Vue 2 Composition API
mascii
4
1.1k
Joy-ConをJavaScriptでプレゼンリモコンにした話
mascii
0
570
Vue.jsでCSS Modulesを使ってみた
mascii
0
140
不変量
mascii
1
200
Nuxt.js+Firebaseで個人サービスを作るまで
mascii
1
2.4k
JavaScriptのバージョンの話
mascii
1
2.3k
あなたのお家に眠るラズパイを救出したい
mascii
4
3.1k
Other Decks in Programming
See All in Programming
Playwrightはどのようにクロスブラウザをサポートしているのか
yotahada3
7
2.3k
詳しくない分野でのVibe Codingで困ったことと学び/vibe-coding-in-unfamiliar-area
shibayu36
3
4.4k
Go言語の特性を活かした公式MCP SDKの設計
hond0413
1
180
エンジニアとして高みを目指す、 利益を生み出す設計の考え方 / design-for-profit
minodriven
23
12k
私はどうやって技術力を上げたのか
yusukebe
43
17k
CI_CD「健康診断」のススメ。現場でのボトルネック特定から、健康診断を通じた組織的な改善手法
teamlab
PRO
0
180
monorepo の Go テストをはやくした〜い!~最小の依存解決への道のり~ / faster-testing-of-monorepos
convto
2
390
CSC305 Lecture 04
javiergs
PRO
0
250
デミカツ切り抜きで面倒くさいことはPythonにやらせよう
aokswork3
0
190
Чего вы не знали о строках в Python – Василий Рябов, PythoNN
sobolevn
0
160
Your Perfect Project Setup for Angular @BASTA! 2025 in Mainz
manfredsteyer
PRO
0
130
The Past, Present, and Future of Enterprise Java
ivargrimstad
0
140
Featured
See All Featured
The Invisible Side of Design
smashingmag
301
51k
A Tale of Four Properties
chriscoyier
160
23k
The World Runs on Bad Software
bkeepers
PRO
71
11k
StorybookのUI Testing Handbookを読んだ
zakiyama
31
6.2k
Why You Should Never Use an ORM
jnunemaker
PRO
59
9.6k
Build The Right Thing And Hit Your Dates
maggiecrowley
37
2.9k
Thoughts on Productivity
jonyablonski
70
4.9k
What’s in a name? Adding method to the madness
productmarketing
PRO
23
3.7k
[Rails World 2023 - Day 1 Closing Keynote] - The Magic of Rails
eileencodes
36
2.5k
The Pragmatic Product Professional
lauravandoore
36
6.9k
Exploring the Power of Turbo Streams & Action Cable | RailsConf2023
kevinliebholz
34
6.1k
4 Signs Your Business is Dying
shpigford
185
22k
Transcript
None
• • •
• •
None
const user1 = { age: 26, driverLicense: { expirationDate: '2023/01/22'
}, } const user2 = { age: 12, driverLicense: null, } user1.driverLicense.expirationDate // '2023/01/22' user2.driverLicense.expirationDate // TypeError: Cannot read property 'expirationDate' of null
•
https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Operators/Optional_chaining
const user1 = { age: 26, driverLicense: { expirationDate: '2023/01/22'
}, } const user2 = { age: 12, driverLicense: null, } user1.driverLicense?.expirationDate // '2023/01/22' user2.driverLicense?.expirationDate // undefined
• let expirationDate if (user.driverLicense) { expirationDate = user.driverLicense.expirationDate }
None
None
• ◦ https://devblogs.microsoft.com/typescript/announcing-typescript-3-7-rc/
https://devblogs.microsoft.com/typescript/ announcing-typescript-3-7-rc/ http://www.typescriptlang.org/play/
• "use strict"; var _a, _b; const foo = {
bar: null }; // foo?.bar?.baz (_b = (_a = foo) === null || _a === void 0 ? void 0 : _a.bar) === null || _b === void 0 ? void 0 : _b.baz;
• • const foo = { items: ['Pen', 'Pineapple', 'Apple'],
get bar() { console.count('bar!'); return { baz: this.items.join() }; } } foo?.bar?.baz // bar!: 1 // 'Pen,Pineapple,Apple' foo && foo.bar && foo.bar.baz // bar!: 2 // bar!: 3 // 'Pen,Pineapple,Apple'
• • $ npm i typescript@rc ts-node $ npx ts-node
None