特殊类型的隐式转换NaN,0,underfined,null,"" =>默认情况下会转成false,除了这5个之外会是true
var bool = Boolean(NaN);
console.log(bool);//false
逻辑预算福&& 和 || 在隐式转换下的情况
console.log(5 || 0);//5
console.log(0 || 5);//5
console.log(0 && 5);//0
==和===的区别
console.log(underfined == null); //true 隐式转换 都转成0,值相等
console.log(underfined === null); //false 值 类型都相等