jQuery : How to check if a variable is both null and /or undefined in JavaScript

jQuery : How to check if a variable is both null and /or undefined in JavaScript
To Access My Live Chat Page,
On Google, Search for "hows tech developer connect"

I promised to reveal a secret feature to you, and now it's time to share it.
This is a YouTube's feature which works on Desktop.
First, Ensure that the video is playing before proceeding.
Then, type the letters 'awesome' on the keyboard.
Your YouTube progress bar will transform into a flashing rainbow.

A short overview of who I am,
Hey, I am Delphi.
I can assist you in discovering answers to your inquiries.
jQuery : How to check if a variable is both null and /or undefined in JavaScript
I encourage you to reach out through comments or chat if you have more specific questions.
If you have additional information or an answer to contribute, please feel free to comment below.
I will express my appreciation for your answer by 'hearting' it.
check a JavaScript to in null and variable How undefined jQuery is both : if /or