在Javascript中，对象和数组是两种基本的数据类型，而且它们也是最重要的两种数据类型。
对象是已命名的值的一个集合，而数组是一种特殊对象，它就像数值的一组有序集合。
4.1 关联数组的对象 Objects as Associative Arrays
对于对象，其属性相当于已命名的字符串值的一个集合。可以使用数组存取运算符[]来提取属性。
对象可以使用"."来存取一个对象属性，而数组更常用的存取属性运算符是[].下面两个表达式等效：
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以上两种方式的重要区别是：前者的属性名是标识符，后者的属性名却是一个字符串。★
以下原文说明了它的重要性：
In C, C++, Java, and similar strongly typed languages, an object can have only a fixed number of properties, and the names of these properties must be defined in advance. Since JavaScript is a loosely typed language, this rule does not apply: a program can create any number of properties in any object. When you use the . operator to access a property of an object, however, the name of the property is expressed as an identifier. Identifiers must be typed literally into your JavaScript program; they are not a datatype, so they cannot be manipulated by the program
On the other hand, when you access a property of an object with the [] array notation, the name of the property is expressed as a string. Strings are JavaScript datatypes, so they can be manipulated and created while a program is running. So, for example, you can write the following code in JavaScript:
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4.2 通用的object属性和方法
① constructor属性
引用该属性初始化对象的构造。
② toString()方法
把对象转换成字符串时，就会调用这个方法
③ toLocalString()方法
返回一个本地化字符串表示
④ valueOf()方法
与toString()方法很像，它是当Javascript把一个对象转换为某种基本数据类型，即数字而非字符串时，调用的方法
默认的valueOf并不做什么有意义的事情。
⑤ hasOwnProperty（）方法
The hasOwnProperty() method returns true if the object locally defines a noninherited property with the name specified by the single string argument. Otherwise, it returns false. For example:
也即是说，如果参数中指定的字符串，相当于对象的一个属性，该属性在本类中实现，返回true,在继承类中实现，返回false.
⑥ propertyIsEnumerable() 方法
如果字符串参数所指定的名字，相当于对象的一个非继承的属性；且属性可以在一个for/in循环中枚举。返回true.
Note that all user-defined properties of an object are enumerable.(一个对象的所有用户定义的属性都是可以枚举的。) Nonenumerable properties are typically inherited properties (see Chapter 9 for a discussion of property inheritance), so this method almost always returns the same result as hasOwnProperty().
⑦ isPrototypeOf()方法
The isPrototypeOf() method returns true if the object to which the method is attached is the prototype object of the argument. Otherwise, it returns false. For example: