!!でbool値変換
function Account(cash){ this.cash = cash; this.hasMoney = !!cash; } var account = new Account(98); console.log(account.cash); //98 console.log(account.hasMoney); // true var emptyAccount = new Account(0); console.log(emptyAccount.cash); //0 console.log(emptyAccount.hasMoney); // false
+文字列を数値に変換
function toNumber(strNumber){ return +strNumber; } console.log(toNumber("1234")); // 1234 console.log(toNumber("ABC")); //NaN
&& 条件式
if (connected){ login(); } // ↑の式のを以下のように書ける connected && login(); // 以下のようにuserオブジェクトの存在チェックにも user && user.login();
||でデフォルト値設定
function User(name, age) { this.name = name || "Hoge"; this.age = age || 30; } var user1 = new User(); console.log(user1.name); // Hoge console.log(user1.age); // 30 var user2 = new User("Boa", 25); console.log(user2.name); // Boa console.log(user2.age); // 25
配列切断
var array = [1,2,3,4,5,6]; console.log(array.length); // 6 array.length = 3; console.log(array.length); // 3 console.log(array); // [1,2,3]
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