JS foundation -- object static method

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One 、Object Static methods

Static methods are methods that are called directly using the class name
object What are the static methods in ？

1.getPrototypeOf()

Object.getPrototypeOf() Get the prototype of the object , amount to obj._proto_

			function fn () {
				
			}
			fn.prototype=["ljy",22]
			var obj=new fn()
			var re=Object.getPrototypeOf(obj)//==>obj.__prto__
			console.log(re)

2.getOwnPropertyNames()

Object.getOwnPropertyNames() take obj The names of enumerable and non enumerable attributes of form an array and return

			var obj=[10,203,4]
			var re=Object.getOwnPropertyNames(obj)
			console.log(obj,re)

3.keys()

Object.keys() Returns an array of enumerable properties of a given object , The property names in the array are arranged in the same order as those returned by normal loop traversal of the object .

			var obj={name:'akren',age:20}
			var re=Object.keys(obj)
			console.log(re)

4.values()

Object.values() Method returns an array of all enumerable property values of the given object itself , Order and use of values for…in The order of the cycles is the same ( The difference lies in for-in Loop through the properties in the prototype chain ).

			var obj={name:'ljy',age:22}
			var re=Object.values(obj)
			console.log(re)

5.defineProperty()

Object.defineProperty() Method defines a new property directly on an object , Or modify the existing properties of an object , And return this object .
You can define multiple values at once .

The descriptor	effect
configurable	If and only if the configurable The key value is true when , Only the descriptor of this property can be changed , At the same time, this attribute can also be deleted from the corresponding object . The default is false.
enumerable	If and only if the enumerable The key value is true when , This property will appear in the enumeration property of the object . The default is false.
value	The value corresponding to this property . It can be anything that works JavaScript value （ The number , object , Functions, etc ）. The default is undefined.
writable	If and only if the writable The key value is true when , The value of the property , That's the top value, Can be changed by the assignment operator . The default is false.
get	Attribute getter function , without getter, Then for undefined. When accessing this property , This function will be called . No parameters are passed in during execution , But it will pass in this object （ By inheritance , there this It does not have to be the object that defines the property ）. The return value of this function will be used as the value of the property . The default is undefined.
set	Attribute setter function , without setter, Then for undefined. When the property value is modified , This function will be called . This method takes a parameter （ That is, the new value given ）, The this object . The default is undefined.

Case study 1：

         var obj={}
		 var temp;
		 Object.defineProperty(obj,"ljy",{
			 set(arg){                            // Set the stored data 
				 temp=arg;
				 console.log(" You deposited "+arg)   // When we save this attribute, we print (" You deposited "+arg)
			 },
			 get(){                     // Get stored data 
				 return temp+' year '  // When we get the data of this attribute, we return temp+' year '
			 }
		 })
		 obj.ljy=22
		 console.log(obj['ljy'])

Case study 2：

         var obj={}
		 Object.defineProperty(obj,"ljy",{
			 enumerable:true,
			 value:666,
			 writable:false,   //value Will not be changed by the assignment operator 
		 })
		 obj.ljy=22
		 console.log(obj['ljy'])

6.create()

Object.create() Method creates a new object , Use existing objects to provide prototypes of newly created objects . Also known as factory functions .

			var obj = Object.create([10,20,30],{'ljy':{     // The first parameter represents the prototype , The second parameter represents the object attribute and attribute value description defineProperty() equally .
				value:22,
				writable:false
			}});
			console.log(obj)   // Printed Array The representative prototype is an array 

7.getOwnPropertyDescriptor(obj,propName)

Object.getOwnPropertyDescriptor() Method returns a self owned property on the specified object (propName) The corresponding property descriptor .（ Self owned attribute refers to the attribute directly assigned to the object , Properties that do not need to be looked up from the prototype chain ）

			 var obj={name:"karen"}
			 var f1=Object.create(obj,{life:{
			 	value:'ljy'
			 }})
			 console.log(f1)
			var re=Object.getOwnPropertyDescriptor(f1,"life")
			console.log(re)

8.preventExtensions(obj)

Object.preventExtensions() Method makes an object non extensible , That is, you can never add new attributes .

			var obj={ljy:22}
			Object.preventExtensions(obj)
			obj.age=200
			console.log(obj,obj.age)

9.seal()

Object.seal() Method to close an object , Prevent adding new properties and marking all existing properties as non configurable .
The value of the current property can be changed as long as it is writable .

			  var obj={ljy:22}
			  var re=Object.seal(obj)
			  obj.age=22
			  delete obj.ljy
			  console.log(obj)

10.freeze(obj)

It can be forbidden to obj All operations , It's relative to preventExtensible In terms of method , Attribute's configurable Properties and writable Properties are set to false.

			var obj={ljy:22}
			var re=Object.freeze(obj)
			delete obj.ljy
			obj.ljy=100
			obj.age=20
			console.log(obj)

11. Determine whether a method is set

Object.isExtensible(obj)、Object.isSealed(obj)、Object.isFrozen(obj) It corresponds to whether the above three methods are correct obj Set up

			var obj={ljy:22}
			var re=Object.freeze(obj)
			delete obj.ljy
			obj.ljy=100
			obj.age=20
			console.log(obj,Object.isFrozen(obj))