Javascript类中的静态变量

Question

是否有正确的方法来创建私有静态javascript变量(和函数),无论您创建多少次都不会更改new Obj？

这是我尝试过的,它似乎工作:

var ObjClass = (function(){

    var static_var = 0; //private static variable
    var static_fn = function(){ return static_var; }; //private static function

    return function(){
        ++static_var;
        var thisNumber = static_var;
        this.getThisNumber = function(){
             return thisNumber;
        }
        this.getStaticNumber = static_fn; //making static fn public
    }

})();

var obj1 = new ObjClass;
var obj2 = new ObjClass;
var obj3 = new ObjClass;

console.log(obj1.getThisNumber()); //output `1`
console.log(obj1.getStaticNumber()); //output `3`
console.log(obj2.getThisNumber()); //output `2`
console.log(obj2.getStaticNumber()); //output `3`
console.log(obj3.getThisNumber()); //output `3`
console.log(obj3.getStaticNumber()); //output `3`?

DEMO

或者还有其他 更好的方法吗？

Answer 1

是的,这是创建私有静态变量的正确方法.

但是,我会对待static_fn不同的.看来你希望它是公开的.

1. 它应该在你的"类"es原型上,因为它不与私有实例变量交互
2. 它甚至根本不与实例交互.通常的approch是将这样的函数/变量放在"类"本身,即JS中的构造函数.由于构造函数是一个Function对象,因此可以使用任何其他js对象的属性进行扩展.

var ObjClass = (function closure(){

    var static_var = 0; //static private (scoped) variable
    function static_fn(){ return static_var; }; //static private (scoped) function

    function ObjClass() {
        var thisNumber = ++static_var; // private instance variable
        this.getThisNumber = function() { // public instance method
            return thisNumber; // "privileged" to access scoped instance variables
        };
    }
    ObjClass.getStaticNumber = static_fn; // make the static_fn public
    return ObjClass;
})();



var obj1 = new ObjClass;
var obj2 = new ObjClass;
console.log(ObjClass.getStaticNumber()); //output `2`
var obj3 = new ObjClass;
console.log(ObjClass.getStaticNumber()); //output `3`

console.log(obj1.getThisNumber()); //output `1`
console.log(obj2.getThisNumber()); //output `2`
console.log(obj3.getThisNumber()); //output `3`