In the spirit of the holiday season, this is a series of short blog posts covering random things I have learned while doing Salesforce development, one for each day of Advent.

Jack skellington
JavaScript Town isn't nearly as exciting

The “this” keyword can be hard to wrap your head around, and I personally have wrestled with it for a long time (which makes me think it’s a language problem and not my fault! But I digress). So while I was trying to learn how to use it, I found it was much more fun to sing about it!

Here’s a song I wrote a few years ago about this:


(to the tune of ‘What’s This?’ From The Nightmare Before Christmas)

What's this, what's this?
My scope is everywhere.
What's this?
And now it isn't there.

What's this?
Call, apply and bind,
What am I typing
setTimeout? This isn't fair!
What's this?

What's this? What's this?
I guess I'll check this blog
What's this?
Now try console.log()

What's this?
The code is lined with
debugs laughing
breakpoints trying to see what's happening
Have I possibly gone daffy?
What is this?

What's this?

There's functions throwing exceptions
undefined it said
Suddenly it's working
And now my code is dead

this is equal to the window?
Oh, I can't believe my eyes
This async function has a new
scope coming from inside...

Alert! What's this?
They're binding to the scope! Var that?
That is still defined! Inspired!
This is set to that to keep this constant
Every single time it fires
What's this?

What's this?
Right here! A method named call? How queer
And who would ever think?

This is bound to all sorts of things
Following a call stack like a string
And there's a smile on everyone
So now correct me if I'm wrong

This is dumb!
This is fun!
Oh, could it be I got my wish?
What's this?

Oh my, what now?
A callback argument?
But look, call() cannot be sent
Or apply(), no parameters to declare them
Or ensnare them, but bind() ensures that they are
Defined inside this function... hmm....

What's this?

This is still just missing
The scope cannot be found
And in their place there seems to be
Undefined's all around

Instead of binding correctly
Another var I have to declare
The sight of programs crashing
Are absolutely everywhere

The stacks, the calls!
They're everywhere and all, around
I never felt so confused, before!
This implied scope keeps hoisting up
I simply cannot get this function up

I want this, oh I want this
I want this to be known
I've got to know, I've got to know
Is there a syntax that is sound?
What! Is! This!

Arrow functions? Hmm…