JS's OOP < two > object properties

The object properties in JS can be added and deleted dynamically. Delete The object property with the delete keyword.

    function obj () {  }    varnew  obj ();     = "a";     = "B";     // output a    // Output B    Delete oo.a;     // output undefined

In JS, the properties of an object are represented by key-value pairs, and are unordered (over time). The attribute name ( i.e. key) in JS can be accessed ( or assigned) with a dot, or it can be accessed ( or assigned ) with the Bracket key value (the key must be of type string when accessing the object property with the bracket key) )

var a = {x:5,y:2//a[' x '];   Output 5

There are two ways to traverse object properties, which are commonly used to traverse object properties.

var obj = {a1:1, a2:2, A3:3, A4:4, A5:5 };  for (var i=1;i<=5;i++ ) {    console.log (obj[' a ' + i]);} // Output 1 2 3 4 5

var obj = {a:1, b:2, C:3, D:4, E:5 };  for (var in obj) {    console.log (Obj[item]);} // Output 1 2 3 4 5

It is important to note that for-in traversal object properties are unordered and may traverse properties on the prototype chain. And you can only use the [] Read property when using for in traversal, you cannot use. read.

functionObj_pro () {}//creating the Obj_pro constructorOBJ_PRO.PROTOTYPE.F = 55;//Create Obj_pro prototype properties Fvarobj =NewObj_pro ();//Obj_pro Creating an Obj object//obj object property Loop Assignment for(vari=1;i<=5;i++) {obj[' A ' + i] = (i+9);}//traversing obj Object Properties for(varIteminchobj) {Console.log (Obj[item]);}//Output 10 11 12 13 14 55 Here's a traversal of the property F on the prototype chain .

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Get/set of attributes

Get/set, like other languages, is used to encapsulate object properties. Get settings read, set set write.

var person = {    name:' Mirage ',    get Age () {        return age ;    },    set Age (val) {        if(val < 0 | | IsNaN (val) | | val >) {            =;        }  Else{            = val;        }     = -99; console.log (person.age);     // Output

The value of age can be judged in set, as well as in get.

var person = {    name:' Mirage ',    get Age () {        if' < 0 | | IsNaN (age) | | Age >) {            return ;        } Else {            return  Age        }    },    set Age (val) {        = val;     = -99; console.log (person.age);    // Output

You can set specific properties to read-only or unreadable through Get/set

var player = {    get Gameyear () {        return 5;     =Console.log (player.gameyear);    // Output 5

Only the Get return value is set, and the property is not modifiable ( read-only ).

var player = {    set Age (val) {        if(val < 0 | | IsNaN (val) | | val >) {            =;        } Else {            = val;        }     = "Age";      // player.pname value isconsole.log (player.age);  // output undefined

Set only, this property can be modified but not readable.

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The Get/set of the prototype chain

Object.defineproperty is required to set the Get/set property for the object created by the constructor.
The object.defineproperty function can add object properties and modify the attributes of an existing property.
object.defineperperty Parameters:
　　Object (required): The target object (which can also be added to the object's prototype, as well as a DOM object). type:ObjectName(object name).
　　PropertyName (required): property name. type:String (string).
　　Descriptor (required): Property descriptor. type:Object _ literal.

functionPerson () {}object.defineproperty (Person.prototype,"Age", {get:function(){                            returnAge ; }, set:function(val) {if(val < 0 | | | IsNaN (val) | | val > 150) { age= 18; }Else{ Age=Val; }                        }                      });varP1 =NewPerson ();p 1.age= 6150; Console.log (p1.age); //output 18. 

The object prototype properties can be modified by DefineProperty.

JS's OOP < two > object properties