javascript - 如何在javascript中定义私有(private)构造函数？

Question

我在 JS 中定义了纯对象，它公开了某些应该用于构造它们而不是构造函数的静态方法。如何在 Javascript 中为我的类创建一个私有(private)的构造函数？

var Score = (function () {

  // The private constructor
  var Score = function (score, hasPassed) {
      this.score = score;
      this.hasPassed = hasPassed;
  };

  // The preferred smart constructor
  Score.mkNewScore = function (score) {
      return new Score(score, score >= 33);
  };

  return Score;
})();

更新:解决方案应该仍然允许我测试 x instanceof Score。否则，@user2864740 仅公开静态构造函数的解决方案有效。

Answer 1

可以在闭包内使用变量(initializing)，如果直接调用构造函数而不是通过类方法调用，则可能会抛出错误:

var Score = (function () {
  var initializing = false;

  var Score = function (score, hasPassed) {
      if (!initializing) {
         throw new Error('The constructor is private, please use mkNewScore.');
      }

      initializing = false;
      this.score = score;
      this.hasPassed = hasPassed;
  };

  Score.mkNewScore = function (score) {
      intializing = true;
      return new Score(score, score >= 33);
  };

  return Score;
})();