js实现单例模式

容易被忽略的地方，是类的原型。所以在构造函数里，需要小心

function Universe()
{
    // the cached instance
    var instance;
    // rewrite the constructor
    Universe = function Universe() {
      return instance;
    };
    
    // carry over the prototype properties
    Universe.prototype = this;
    // the instance
    instance = new Universe();
    // reset the constructor pointer
    instance.constructor = Universe;
    // all the functionality
    instance.start_time = 0;
    instance.bang = "Big";
    return instance;

};

var uni = new Universe();
var uni2 = new Universe();

if (uni == uni2)
{
  console.log('same');
  uni.bang = 'hay';
  console.log(uni2.bang);
}
else
  console.log('diff');