Javascript and singleton pattern

问题

I am reading the book by Addy Osmani book, Learning Javascript design patterns. http://addyosmani.com/resources/essentialjsdesignpatterns/book/

I have created a file called singleton.js it contains:

var mySingleton = (function() {
var instance;

function init() {

    var privateRandomNumber = Math.random();

    return {
        getRandomNumber : function() {
            return privateRandomNumber;
        }
};


return {
    getInstance : function() {
        if (!instance) {
            instance = init();
        }
        return instance;
    }
};


})();

I have a file that uses this mySingleton class, in that file I have

var mySin = require('./util/ss_client');
var singleB = mySin.getInstance();

I get a compile error saying var singleB = mySin.getInstance();

I missed something in the ss_client file to export mySingleton class?

回答1:

Yes, you need to export mySingleton by assigning it to module.exports. You also have a syntax error in your code (one of your braces is in the wrong place). Fixing those two things, you get:

var mySingleton = (function() {
  var instance;

  function init() {
    var privateRandomNumber = Math.random();

    return {
      getRandomNumber : function() {
        return privateRandomNumber;
      }
    };
  }

  return {
    getInstance : function() {
      if (!instance) {
        instance = init();
      }
      return instance;
    }
  };

})();

module.exports = mySingleton;

来源：https://stackoverflow.com/questions/20061157/javascript-and-singleton-pattern