js隐式轉換及包裝類型

var x = '33';
           

//很巧妙的類型轉換
console.log(typeof (x - 0));//number
console.log(typeof (x + ''));//string

var str = new String();
console.log(str.length);//仍為0,調用的是String包裝類的length屬性
           

str.t = 1;
           

console.log(str.t);//undefined