[JavaScript] New-Agnostic Constructor Pattern

function User (name, password) {
  var self = this instanceof User ? this : new User();

  if (name != null) {
    self.name = name;
    self.password = password;
  }
  return self;
};

var obj1 = User("andy","");
var obj2 = new User("andy","");
console.log(obj1.name === obj2.name); // return true;

这样可以防止漏写new，导致的错误。