JS Objects and Classes

• JS Object category

  1. Built-in objects such as array Date Function
  2. Host objects such as windows in the browser
  3. Custom Object The user creates in the code

• The composition of the object

  1. Property

     Differentiate by inheritance

     • Own property
     • Inheriting properties defined in the Property object prototype

     By category

     • Data properties
     • Accessor properties
       

       var o = {    get name() {},    set name(value) {},}

  2. Three Object attributes

     • Object Prototype prototype
     • Class of Object
     • Extension tags for objects

• Attribute Properties

  2. Data attribute Attribute value,writable,enumerable,configurable
  4. Accessor attribute get,set,enumerable,configurable

  6. Property Descriptor

     // return {value:1,writable:true,enumrable:true,configurable:true}  Object . Getownpropertydescription ({x:1 }, "x" ); //returns undefined   

  for non-existent and inherited properties

  8. Set property properties

      var  o = {}; object . DefineProperty (O, "x" , {Value:1 , Writable:true , Enumrable:false , Configurable:true }) / /modified to read-only  object . DefineProperty (O, "x" , { Writable:false }) o.x = 2 ; //error  //but the properties are still configurable, so you can modify the value of x  object . DefineProperty (O, "x" , {Value:2 }); 

• Property manipulation

  1. Delete Deletes the property, but only the free attribute is deleted

  2. Detection properties

     //in操作符var o = {x:1};"x"in o;//会从自有属性和继承属性中判断o.hasOwnProperty("x");//只会检测自有属性o.propertyIsEnumerable("x");//检测自有属性，且可枚举性为true，可枚举性是属性特性之一

• Object prototypes

  Each JS object has a prototype object (except NULL and Object.prototype)

  varnewObject();var a = {};//两种方式的原型都是Object.prototype//此处的Object并不是 java等语言中 类的概念，而是Object构造函数

  A prototype object is a unique indicator of a class

  var o = {x:1,y:1};function A {}A.prototype = o;function B {0;newinstanceof A// true 虽然new A() 和 new B()是不同的构造函数产生的，但是他们的原型都是o

  Object.create () a static function with two parameters, the first to create a prototype of the object

  var  O1 = object . Create ({x:1 , Y:2 }); //inherited attributes X, y  var  o2 = object . Create ( null ); //create an object without a prototype, without any method, including the ToString  var  O3 = object . Create ( object . prototype); //with var a = {}   

• Constructor Property

  1. Prototype object for each function has a constructor property

     var  F = function  f   ()  {}< Span class= "Hljs-keyword" >var  p = f.prototype;
       var  c = p.constructor;c = = = F;  

  The

  2. Constructor is the same

      var  o = new  F (); //o inherits F.prototype  O.constructor = = = F;
      //true   

• Extensible markup for objects

  Object.isExtensible(o);//判断对象是否可拓展Object.preventExtensions(o);//设置为不可拓展，该过程不可逆，但是给o的原型增加属性，o仍然可以继承这些属性Object.isSealed(o);Object.seal(o);//不可拓展，并设置自有属性为不可配置Object.isFrozen()Object.freeze();//不可拓展，并设置自有属性为不可配置，属性设置为只读，setter 属性不受影响

• Object serialization is converting to a JSON string

  JSON.stringify(o);JSON.parse();

• Classes and Types

  typeof//对于对象都返回Objectfunction classof(o) {    returnObject.prototype.toString.call(o).slice(8,-1);}//可以返回内置对象的具体类型 比如Date RegExp等

  Both of these methods have limitations, so how do you get the type of the custom object?

  1. Using instanceof
  2. Constructor property
     

     function typeAndValue(x) {    ifnull)return"";    switch(x.constructor) {        caseNumber:return"Number:"+x;        case Complex:return"Complex:"+x;//处理自定义类型    }}

JS Objects and Classes