用闭包创建的私有函数如何访问构造函数中定义的变量？

Question

I have the following code :

var TagCloud = (function() {
  var createTagsArray = function() {
    j$("#" + this.cloudId + " a").each(function(index) {
      //bla bla
    });
  }

  function TagCloud(cloudId) {
    this.cloudId = cloudId;
  };

  TagCloud.prototype.createTagCloud = function(){
    createTagsArray(this.cloudId);            
  };

  return TagCloud;
}());

new TagCloud("tagcloud");

I create TagCloud object. I create it with closure to have a private function createTagArray . However inside this function I would have an access to variable defined in TagCloud constructor - cloudId . Of course in this example I cannot get it using this . But is there anyway to get it ? (I wouldn't like to pass this value as function createTagArray parameter).

It can be also my mistake in understanding usage of closure, because I've started working with closures.

Answer 1

You cannot access the variable through closure, for that you would need to define the createTagsArray function within the TagCloud constructor function - and then you couldn't access it from the createTagCloud method any more without making it public.

But I don't think you want access to the variable anyway. You want access to the .cloudId property of your instance, and for that you need the instance.

Passing it - either the property value or the complete instance - as a parameter would be preferred actually. There's nothing wrong with that:

var createTagsArray = function(cloudId) {
  j$("#" + cloudId + " a").each(function(index) {
    //bla bla
  });
}
TagCloud.prototype.createTagCloud = function(){
  createTagsArray(this.cloudId);
};

And using call you could even pass the instance itself so that you can access it as this :

var createTagsArray = function() {
  j$("#" + this.cloudId + " a").each(function(index) {
    //bla bla
  });
}
TagCloud.prototype.createTagCloud = function(){
  createTagsArray.call(this);
};

From there you could even easily switch (back and forth) to a semi-private method:

TagCloud.prototype._createTagsArray = function() {
  j$("#" + this.cloudId + " a").each(function(index) {
    //bla bla
  });
}
TagCloud.prototype.createTagCloud = function(){
  this._createTagsArray();
};

Answer 2

Try following code:

 function TagCloud(cloudId) { var self = this; self.createTagsArray = function() { console.log(this); } self.cloudId = cloudId; self.createTagCloud = function() { self.createTagsArray() } return{ "cloudId": cloudId, "createTagCloud": self.createTagCloud } }; var obj = new TagCloud("tagcloud"); obj.createTagCloud(); var obj = new TagCloud("TagCloudTest"); obj.createTagCloud();