Error when calling function within array of its own prototype (js)

Question

Sorry if this is a dumb question I'm just experimenting and don't understand why this doesn't work:

var MyFunc = function() {};                                                    

MyFunc.prototype = {                                                           
  receive: function() {                                                        
    console.log("Received");                                                   
  },                                                                           
  spine: [MyFunc],                                                             
}                                                                              

var func = new MyFunc();                                                       

func.receive();          //works                                               
func.spine[0].receive(); //error: Object function () {} has no method 'receive'

The last line is the error line.

Full output:

Received

/home/zxcv/Documents/CODE/js/stuff/gp/scratch.js:13
func.spine[0].receive(); //error: Object function () {} has no method 'receive
              ^
TypeError: Object function () {} has no method 'receive'
    at Object.<anonymous> (/home/USER/Documents/CODE/js/stuff/gp/scratch.js:13:15)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:929:3

shell returned 8

Because at the time of assignment myFunc is still only a function with no inherited method. — Mohit Pandey
– Mohit Pandey, Commented Aug 22, 2015 at 16:46

Patrick Evans · Accepted Answer · 2015-08-22 16:53:19Z

3

Because spine[0] is MyFunc (the constructor function object), not an instance object of MyFunc. Functions defined in prototype get put on the instances created by the constructor not on the constructor itself.

You would have go through the prototype in order to execute the function

func.spine[0].prototype.receive();

If you were wanting to create a method that you could execute directly from MyFunc you would need to actually define it on MyFunc

MyFunc.receive2 = function(){
    console.log("Received");
};
var func = new MyFunc();
func.spine[0].receive2();
//Or
MyFunc.receive2();

//Note you would not be able to call this directly from the instance
func.receive2(); //would cause an error

edited Aug 22, 2015 at 16:53

answered Aug 22, 2015 at 16:46

Patrick Evans

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