实现某个类的静态方法，调用后可得到此构造函数/class已经new了多少个实例？

Question

调用：ClassA.getInstanceNumber()

Answer 1

呐，这是es6不用装饰器node和最新chrome可用版

class ClassA {

  constructor() {

    ClassA.instanceNumber = (ClassA.instanceNumber || 0) + 1;

  }

  static getInstanceNumber() {

    return ClassA.instanceNumber || 0;

  }

}

console.log(ClassA.getInstanceNumber());

let a = new ClassA();

console.log(ClassA.getInstanceNumber());

let b = new ClassA();

console.log(ClassA.getInstanceNumber());

Answer 2

看起来比较适合用 ES6 的修饰器 来做。

@countable

class ClassA {

  // ....

}

let count = 0;

function countable() {

  count++;

}

Answer 3

var Test = (function () {

    var count = 0;

    function Test() {

        if (!(this instanceof Test)) {

            return new Test();

        }

        count++;

    }

    Test.getInstanceNumber = function () {

        return count;

    }

    return Test;

})();

Test();

new Test();

new Test();

console.log(Test.getInstanceNumber());//3