Question

我可以算一个物体吗？像：

 var student1 = new Student();
student1.name("ziv");
student1.age();
student1.where("a");


 var student2 = new Student();
student2.name("dani");
student2.age();
student2.where("b");

 var student3 = new Student();
student3.name("bari");
student3.age();
student3.where("c");

一些将计算它们并返回3的函数。

谢谢：）

Answer 1

我想你的意思是计算实例。您必须跟踪实例，例如使用数组

var students = [];
var student1 = new Student()
   ,student2 = new Student();
students.push(students1,students2);
/* later ... */
var nOfStudents = students.length; //=> 2

另一个想法是为Student原型添加一个计数器：

Student.prototype.instanceCnt = 0;

并在每个实例的学生构造函数中递增它

   //in the Student constructor function
   function Student(){
     this.instanceCnt += 1;
     /* ... */
   }
   // usage example
   var student1 = new Student()
      ,student2 = new Student()
      ,students = student1.instanceCnt; //=> 2

Answer 2

不，您需要在Student构造函数中手动添加计数器，或将每个实例附加到数组并获取该数组的长度。

F.ex：

var counter;
function Student() {
    counter++; // this will increase every time Student is initialized
    // continue the constructor...
}

或者：

var students = [];
function Student() {
    students.push(this); // this will hold the instance in an array
    // continue the constructor...
}
console.log(students.length);

Answer 3

Javascript中没有静态概念，但您可以使用闭包来模拟该功能。

(function(){

  var numberOfInstances = 0;

  var Student = function(studentName){
    var name = '';

    var _init(){
      name = studentName ? studentName : 'No Name Provided';
      numberOfInstances++;    
    }();

    this.getName = function(){
       return name;
    }; 

    this.getNumberOfInstances = function(){
      return numberOfInstances;
    };

    return this;
  };
})(); 

var student1 = new Student("steve");
var student2 = new Student("sally");
console.log("my name is " + student1.getName());
console.log("my name is " + student2.getName());
console.log("number of students => " + student1.getNumberOfInstances());  
console.log("number of students => " + student2.getNumberOfInstances());

Answer 4

您可以编写一个简单的通用实例化/继承帮助程序来跟踪其在数组中的实例

这样的事可能会这样做

var base = (function baseConstructor() {

  var obj = {
    create:function instantiation() {
        if(this != base) {
        var instance = Object.create(this.pub);
         this.init.apply(instance,arguments);
         this.instances.push(instance);
        return instance;
        } else {
          throw new Error("You can't create instances of base");
        }
    },
    inherit:function inheritation() {
      var sub = Object.create(this);
      sub.pub = Object.create(this.pub);
      sub.sup = this;
      return sub;
    },
    initclosure:function initiation() {},
    instances: [],
    pub: {}

  };



  Object.defineProperty(obj,"init",{
   set:function (fn) {
     if (typeof fn != "function")
       throw new Error("init has to be a function");
     if (!this.hasOwnProperty("initclosure"))      
       this.initclosure = fn;
    },
    get:function () {
        var that = this;
        //console.log(that)
            return function() {
              if(that.pub.isPrototypeOf(this)) //!(obj.isPrototypeOf(this) || that == this))
                that.initclosure.apply(this,arguments);
              else
                throw new Error("init can't be called directly"); 
             };
    }    

  });


  Object.defineProperty(obj,"create",{configurable:false,writable:false});
    Object.defineProperty(obj,"inherit",{configurable:false,writable:false});
  return obj;
})();

var Student = base.inherit()
    Student.init = function (age) {
    this.age = age;    
    }

var student1 = Student.create(21)
var student2 = Student.create(19)
var student3 = Student.create(24)

    console.log(Student.instances.length) // 3

以JSBin

为例

是否可以将对象计为“整体”？

4 个答案: