What are the three properties of a javascript object?

This time I will bring you javascript objectwhat are the three attributes, what are the notesof the three attributes of javascript object, the following is a practical case, let's take a look.

Each object has a prototype, class, and extensible attribute associated with it.

Prototype property

The prototype property of an object is used to inherit properties.
The prototype property is set at the beginning of the creation of the instance object. The object created through the object directly uses Object.prototype as their prototype. Objects created through new use the prototype attribute of the constructor as their prototype. Objects created through Object.create() use the first parameter (which can also be null) as their prototype.

* 检测一个对象是否是另一个对象的原型（或处于原型链中），使用isPrototypeOf()方法  var p = { x: 1 };  var o = Object.create(p);
  p.isPrototypeOf(o)； // true
  Object.prototype.isPrototypeOf(o);  // true

Class attribute

The class attribute of an object is a string that represents the type information of the object.
To get the class of the object, you can call the toString() method of the object, and then extract the string between the 8th and the penultimate position of the returned string. However, many objects inherit 's toString() method and override it. In order to call the correct toString() version, the Function.call() method must be called indirectly.
eg:

   function classof(o) {        if(o === null) return "Null";        if(o === undefined) return "Undefined";        return Object.prototype.toString.call(o).slice(8,-1);
    }

Extensibility

The extensibility of an object indicates whether new properties can be added to the object. All built-in objects and custom objects are explicitly extensible, as defined by the host object's extensibility roommate, the JavaScript engine. In ECMAScript 5, all built-in and custom objects are extensible unless they are converted to non-extensible. Likewise, the extensibility of host objects is defined by the JavaScript engine that implements ECMAScript 5.

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