if文のはなし

Transcript

1. if文のはなし @ticktakclock
2. 自己紹介 • 竹中貴哉 @ticktakclock • React, Cordova • javascript 始めて 6 ヶ月経ちました • 本業は Android
3. if ...
4. const str = 'we are javascripters'; console.log(`length: ${str.length}`); if (str.length > 0) { // true console.log('ok'); } // > length: 20 // > ok
5. const str = 'we are javascripters'; if (str.startsWith('we')) { // true console.log('ok'); } // > ok
6. if文はtrue/falseで判定するんだ！
7. const str = 'we are javascripters'; console.log(str); if (str) { console.log('ok'); } // > we are javascripters // > ok
8. const str = 'we are javascripters'; console.log(str); if (str !== null) { console.log('ok'); } // > we are javascripters // > ok
9. const str = 'we are javascripters'; console.log(str); if (str) { console.log('ok'); } // > we are javascripters // > ok
10. ドキュメント https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Statements/if...else#Syntax
11. truthy? falsy?
12. truthy https://developer.mozilla.org/ja/docs/Glossary/truthy
13. const str = 'we are javascripters'; console.log(str); if (str !== null) { console.log('ok'); } // > we are javascripters // > ok
14. const str = 'we are javascripters'; console.log(str); if (str) { console.log('ok'); } // > we are javascripters // > ok
15. やってみた console.log(0 ? 'truthy' : 'falsy'); // falsy console.log(1 ? 'truthy' : 'falsy'); // truthy console.log(-1 ? 'truthy' : 'falsy'); // truthy console.log('' ? 'truthy' : 'falsy'); // falsy console.log('test' ? 'truthy' : 'falsy'); // truthy console.log(undefined ? 'truthy' : 'falsy'); // falsy console.log(null ? 'truthy' : 'falsy'); // falsy console.log('undefined' ? 'truthy' : 'falsy'); // truthy console.log(new Date() ? 'truthy' : 'falsy'); // truthy
16. まとめ if文の条件式は何でも入る
17. string https://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%201st%20edition,% 20June%201997.pdf
18. おしまい
19. string https://developer.mozilla.org/ja/docs/Web/JavaScript/Data_structures#Strings
20. var str = ''; console.log(str[0]); // undefined console.log(str.length); // 0 console.log(str.charCodeAt(0)); // NaN str = '\0'; console.log(str[0]); // ’ ’ console.log(str.length); // 1 console.log(str.charCodeAt(0)); // 0