# A Javascript prototype question
**URL:** https://discourse.processing.org/t/a-javascript-prototype-question/24699
**Category:** Beginners
**Created:** [October 19, 2020, 7:49am UTC](https://discourse.processing.org/t/a-javascript-prototype-question/24699 "2020-10-19T07:49:45Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@flamo](https://discourse.processing.org/u/flamo)
#### Post date: [October 19, 2020, 7:49am UTC](https://discourse.processing.org/t/a-javascript-prototype-question/24699/1 "2020-10-19T07:49:45Z")
I am currently learning on how to use prototype in JS.
I am curious about what happened after I extended a prototype and then I store the function as variable. why the console.log gives me a _Window_ object for the _canvas_? Why don’t I just get the empty function object i just created?
Here is the code:
```auto
var img = loadImage("/idle.png");
var s = img.splitter();
console.log(s);
p5.Image.prototype.splitter = () => {
// some irrelevant codes here
return this;
}
/** The output in short:
Window {close: function close(), stop: function stop(), focus: function focus(), blur: function blur(), open: function open()…}
*/
```
Thanks.
---
### Author:  [@flamo](https://discourse.processing.org/u/flamo)
#### Post date: [October 19, 2020, 8:24am UTC](https://discourse.processing.org/t/a-javascript-prototype-question/24699/2 "2020-10-19T08:24:17Z")
Oh. I found an answer here:
>
Never mind.
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [October 19, 2020, 8:32am UTC](https://discourse.processing.org/t/a-javascript-prototype-question/24699/3 "2020-10-19T08:32:49Z")
> [@flamo](#):
>
> `p5.Image.prototype.splitter = () => {`
As you’ve already found out just now, creating a function via `=>` syntax binds its `this` permanently to its current context at creation time:
> **[Arrow function expressions - JavaScript | MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions)**
>
> An arrow function expression is a compact alternative to a traditional function expression, with some semantic differences and deliberate limitations in usage:
But method functions need to have their `this` to be the current object which had invoked it at call time:
`p5.Image.prototype.splitter = function () {`
---
### Author:  [@flamo](https://discourse.processing.org/u/flamo)
#### Post date: [October 19, 2020, 8:37am UTC](https://discourse.processing.org/t/a-javascript-prototype-question/24699/4 "2020-10-19T08:37:14Z")
Good answer as always. Thanks. 😇
For the completeness of this thread:
The answer I provide is outdated now. We don’t need `var that = this;` to let `this` refer to the object now. My mistake was to use the “=\>” instead of the function().