How to access methods of parent class inside subclass in javascript

Question

I have a 'model' class/prototype defined as below, it has subclass named 'given' which tries to access method 'getNodes()' of model class.

But it gives exception for 'this.getNodes' saying undefined.

 var model = {
        constructor: function(/*string*/ mode, /*string*/ name, /*object*/ properties) {
            this._mode = mode;
            this.beginX = 100;
            this.beginY = 100;
            this.nodeWidth = 200;
            this.nodeHeight = 200;
            this.x = this.beginX;
            this.y = this.beginY;
            this.lastNodeVisible = null;
            this.ID = 1;
            this.taskName = name;
            this.properties = properties;
            this.checkedNodes = new Array();
      //      this.model = #call_build_method;

            /* 
             add subclasses with model accessors 
             */
            this.given = {
            getNodes: this.getNodes,
            setNodeName: this.setNodeName
        };
      },
      getNodes: function() {
            // Summary: returns an array containing the nodes in the given model 
            return #someobject;
        },
}

When you have a function around `this` think twice. `this` depends on how that function gets called. In your case you need to cache it, like `var self=this` in the higher scope. See http://stackoverflow.com/questions/3127429/javascript-this-keyword — elclanrs, Feb 24 '14 at 23:08
what does it has to do wih dojo? anyway get a basic understanding of the word this in javascript here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this — mpm, Feb 24 '14 at 23:10
You may find this helpful.http://stackoverflow.com/a/16063711/1641941 — HMR, Feb 25 '14 at 05:17

score 1 · Accepted Answer · answered Feb 25 '14 at 22:26

I assume that you want to call a method in the parent class with the correct scope. Here are two ways to do this, one using dojo hitch, and one without:

require([
    "dojo/_base/lang"
],function(lang){
    model = function(){
        var obj = {
            data: "ok",
            getData4: function(){
                return this.data;
            }  
        };

        obj.sub = {
            getData5: lang.hitch(obj, obj.getData4),
            getData6: function(){return obj.getData4.apply(obj,arguments);}
        };

        return obj;
    };

    m = new model();
    console.log("call getData4: ", m.getData4());  // returns "ok"
    console.log("call getData5: ", m.sub.getData5());  // returns "ok"
    console.log("call getData6: ", m.sub.getData6());  // returns "ok"
});

score 0 · Answer 2 · answered Feb 24 '14 at 23:13

0

You need to store this in variable in outter scope:

this.model = <SOMETHING>;
var self = this;
this.given = {
    getNodes: function(){self.getNodes(self.model);}
    // inside a function this is this.given
};

answered Feb 24 '14 at 23:13

jcubic

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How to access methods of parent class inside subclass in javascript

2 Answers2