var obj1 = {};
var obj2 = Object.create(null);
var obj3 = new Object();
var con1 = obj1.constructor;
var con2 = obj2.constructor;
var con3 = obj3.constructor;
console.log(con1);//? Object() { [native code] }
console.log(con2);//undefined
console.log(con3);// Object() { [native code] }
這兩個可以用來判斷js變量是數(shù)組還是對象
console.log(Array.prototype.isPrototypeOf(book[0]));
console.log(Object.prototype.toString.call(book[0]));
