Access an inner function from outside the function in Javascript

Question

I'm trying to access an inner function from outside a function in Javascript, but it only prints "undefined" instead of printing the function's source code. How can I modify the prototype of the function changeBlah from outside the scope of exampleFunction?

var blah = "";
function exampleFunction(theParameter){
   this.blah = theParameter;
    this.changeBlah = function(){
        this.blah += "gah";
    }
}

var stuff2 = new exampleFunction("Heh!");
alert(stuff2.blah);
stuff2.changeBlah();
alert(stuff2.blah);

alert(exampleFunction.changeBlah); //now why doesn't this work? It doesn't print the function's source code, but instead prints undefined.

I just realized that replacing exampleFunction.changeBlah with stuff2.changeBlah prints the function's source. — Anderson Green
– Anderson Green, Commented Oct 2, 2012 at 1:40

Niet the Dark Absol · Accepted Answer · 2012-10-02 01:42:06Z

1

The closest you can get is by using the Prototype model:

function exampleFunction(theParameter) {this.blah = theParameter;}
exampleFunction.prototype.changeBlah = function() {this.blah += "gah";}

alert(exampleFunction.prototype.changeBlah);

answered Oct 2, 2012 at 1:42

Niet the Dark Absol

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score 0 · Accepted Answer · 2012-10-02 02:02:19Z

0

.. now why doesn't [exampleFunction.changeBlah] work?

Because this was not exampleFunction.

It was a new object which had exampleFunction as the [[prototype]]. Assigning to a property does not propagate back up the [[prototype]] resolution chain. (There is no way to access the [[prototype]] of an object directly from an object, but if the [[prototype]] object is known then it can be mutated.)

Compare with (this will break stuff2.blah, but should show exampleFunction.changeBlah working as expected):

exampleFunction.changeBlah = function(){
    this.blah += "gah";
}

(Also see xdazz's comment for another possible access method.)

edited Oct 2, 2012 at 2:02

answered Oct 2, 2012 at 1:41

user166390

1 Comment

xdazz Over a year ago

As the [[constructor]] i think.

Anderson Green · Accepted Answer · 2012-10-02 03:15:05Z

0

This is the best solution that I've devised so far (and it's reasonably concise):

exampleFunction.prototype.changeBlah = function(){
    this.blah += "gah"; //"this" refers to an instance of changeBlah, apparently 
}

var blah = "";
function exampleFunction(theParameter){
   this.blah = theParameter;
}

var stuff2 = new exampleFunction("Heh!");
alert(stuff2.blah);
stuff2.changeBlah(); //it works, even though the "prototype" keyword isn't specifically used here
alert(stuff2.blah);
alert(exampleFunction.prototype.changeBlah);

answered Oct 2, 2012 at 3:15

Anderson Green

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