Checking for the Existence of JavaScript Variables

When writing JavaScript there are going to be times when you want to use a variable or call a function, but you are not sure if it exists, then this is how you can handle these situations.

[shahinza]

Hello Professor! I've truly missed your insightful videos. Your content has always been my go-to for simplifying complex topics. Hoping everything is going well for you. Looking forward to new uploads!

[chiggywiggy]

You're the Bob Ross of programming ❤

[anthonydsouza]

Hi professor. Great to know that you are writing a book. Surely, it's gonna be as awesome as your videos. Wishing you all the best.

[Felipekimst]

Man, that wind out there got me scared lol

[leonardchan]

There's an edge case where, you just declare a variable (but don't assign a value to it) let varname; and typeof varname is actually 'undefined'. So you can't re-declare it. Not practically useful though...

[Strasbourgeois]

A script of type module creates it's own scope preventing var declarations from bubbling up to the global scope

[neerajx]

Hello sir.
You are doing amazing... please upload React

[RedaElMekkaoui-pk]

Hey steve, I'm 15 year old and I only just started learning programming, I want to make it a career out of it, is starting at 15 ideal and how many years will it take me on average to achieve an intermediate or advanced level??

[grenzhochspannungshindernis]

Can you recommend any how-to-program books?

[Fam-mi]

Hi Steve, great content. I was wondering if you could make a video on Promise polyfill using es6 classes. It's commonly asked in interviews

[mayankshashi]

Hi sir, can you please make a video on how we can display image on webpage when we upload image data into indexdb in offline mode?

[RalphGoddard-ttxq]

If your not already, you might want to use a noise cancelling mike