Value of “this” in a JS constructor function returns “undefined”

Question

So i have a constructor function

    var APP = function(name){

        this.appName = name

    }

And a prototype function

    APP.prototype.test = function(){

        console.log(this.appName)

    }

Then i create a new APP() and try out the test function.

    var app = new APP("ieps")
    var testing = app.test

    console.log(app.test()) // returns "ieps"
    console.log(testing()) // returns undefined

Why is it that testing() is returning undefined? testing() should do the same thing as app.test() since i'm just referencing app.test.

Answer 1

You would have to bind the object to the function

var app = new APP("ieps");
var testing = app.test.bind(app);

console.log(testing());

http://jsbin.com/kiyiyutili/2/edit

EDIT: From the MDN docs for .bind :

"The bind() method creates a new function that, when called, has its this keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called."