从附加到原型的对象中访问实例变量

Question

I need to group instance methods into an object before attaching to the protocol But when I do that, "this", now points to the object and I can't access instance variables. Please see the following code for Illustration.

var events = require('events');
var Matcher = function Matcher(){
    this.list3 = [];
    events.EventEmitter.call(this);
};
require('util').inherits(Matcher, events.EventEmitter);

Matcher.prototype.vars = {
  list1 : [ 1, 2 ],
  list2 : [ 'foo', 'bar' ]
};


Matcher.prototype.protocols = {

  print : function(ref){
    console.log(" lists : ", this.list1, this.list2, this.list3 );
  },

  add   : function(item){
    this.vars.list1.push(item);
    this.list3.push(item);
  }

};

var matcher = new Matcher();

matcher.protocols.add( 23 );
matcher.protocols.print();

It gives an error, because this.vars.list1 and this.list3 are both undefined. Most likely because this points to the protocols object and not the prototype.

I would appreciate any help on getting a reference to the variables.

I have tried the following

matcher.protocols.add( matcher, 'new item');

then in the add function i do this, I use matcher in place of this. But this looks wrong to me.

Answer 1

You can rearrange your function definitions to include the definitions within the scope of Matcher . This will allow you to define a private variable equal to this , which you can then access within the vars and protocols definitions.

So for instance:

var events = require('events');
var Matcher = function Matcher(){
    this.list3 = [];
    events.EventEmitter.call(this);

    this.vars = {
      list1 : [ 1, 2 ],
      list2 : [ 'foo', 'bar' ]
    };

    var matcher = this;
    this.protocols = {

      print : function(ref){
        console.log(" lists : ", matcher.vars.list1, matcher.vars.list2, matcher.list3 );
      },

      add : function(item){
        matcher.vars.list1.push(item);
        matcher.list3.push(item);
      }

    };

};
require('util').inherits(Matcher, events.EventEmitter);


var matcher = new Matcher();

matcher.protocols.add( 23 );
matcher.protocols.print();

Outputs:

 lists :  [ 1, 2, 23 ] [ 'foo', 'bar' ] [ 23 ]