if文のはなし@ticktakclock
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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
if ...
const str = 'we are javascripters';console.log(`length: ${str.length}`);if (str.length > 0) { // trueconsole.log('ok');}// > length: 20// > ok
const str = 'we are javascripters';if (str.startsWith('we')) { // trueconsole.log('ok');}// > ok
if文はtrue/falseで判定するんだ!
const str = 'we are javascripters';console.log(str);if (str) {console.log('ok');}// > we are javascripters// > ok
const str = 'we are javascripters';console.log(str);if (str !== null) {console.log('ok');}// > we are javascripters// > ok
ドキュメントhttps://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Statements/if...else#Syntax
truthy? falsy?
truthyhttps://developer.mozilla.org/ja/docs/Glossary/truthy
やってみたconsole.log(0 ? 'truthy' : 'falsy'); // falsyconsole.log(1 ? 'truthy' : 'falsy'); // truthyconsole.log(-1 ? 'truthy' : 'falsy'); // truthyconsole.log('' ? 'truthy' : 'falsy'); // falsyconsole.log('test' ? 'truthy' : 'falsy'); // truthyconsole.log(undefined ? 'truthy' : 'falsy'); // falsyconsole.log(null ? 'truthy' : 'falsy'); // falsyconsole.log('undefined' ? 'truthy' : 'falsy'); // truthyconsole.log(new Date() ? 'truthy' : 'falsy'); // truthy
まとめif文の条件式は何でも入る
stringhttps://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%201st%20edition,%20June%201997.pdf
おしまい
stringhttps://developer.mozilla.org/ja/docs/Web/JavaScript/Data_structures#Strings
var str = '';console.log(str[0]); // undefinedconsole.log(str.length); // 0console.log(str.charCodeAt(0)); // NaNstr = '\0';console.log(str[0]); // ’ ’console.log(str.length); // 1console.log(str.charCodeAt(0)); // 0