var, let and const - What, why and how - ES6 JavaScript Features

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In ES5, we only had one type of variable, var, but in ES6, we have three. types of variables: var, let and const. In this video, we explore the what, why, and how of var, let and const, and I also do a little lecture on the value of minimising mutable state.

► 00:35 var keyword in JavaScript
► 02:35 Immediately-Invoked Function Expression (IIFE) in JavaScript
► 03:14 hoisting variables in JavaScript
► 08:29 let keyword in JavaScript
► 11:55 const keyword in JavaScript
► 14:14 Minimize mutable state when programming

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Resources:

- Semicolons cannot save you! (Another funfunfunction video)

- ES6 JavaScript Features (Playlist of this series)

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[webapplication]

You are the most friendly instructor in the world

[olegon_yt]

TIL: always use 'const'. If you *REALLY* need to change state, use 'let'. 'var' is dead.

Thanks! ;)

[Chocoholic]

Tip for the arm/hand pain: Do hand exercises! Do a YouTube search for 'gaming hand exercise' and you'll find what you need. Just do this every 30-60 minutes for a couple of minutes... you'll notice a world of difference!

Thank you for the video. As always, great content!

[Mikethealtarboy]

Love your videos as always!
I had some arm pain after starting my desk job - mostly in the forearm, and a little tingling around the ring finger. My solution was to make sure my chair was high enough that my arms were 90 degrees with my keyboard, and get a stand for my laptop so I wasn't looking down at it. The source of the problem was actually tight muscles up around my shoulders and neck, which resulted in a nerve being pinched. A little ointment on my shoulder when I found it getting tight helped too. It took a couple months but did get back to normal.

[zsoltoroszlany]

I have to admit I failed to understand what is hoisted ... until now, many thanks for you. I really enjoyed your tutorial video. Thank you again!

[mikeyscimeca]

Thank you so much for making these videos. I have learned so much and have been entertained with your jokes. Thank you Thank You Thank You.

[qwarlockz]

First off of course... thanks so much for your great videos! I really enjoy them. Programmers are getting this now but historically this was a condition that pianists got. This has been topic of conversation for pianists for since the first piano was built. Some of the advice is to have your arm parallel to the floor and to keep your wrist straight (so as to not cut off blood or restrict the nerves) an d to let the weight of your arm or hand coming down (ie gravity) is what provides the force to hit the keys not forcing the arm down. Lots of books on piano technique out there that all programmers should look at.

[SayuStrife]

Brilliant Video. The talk about mutable state will definately help me design my code better going forward.

[adamkucharik]

Another arm pain tip: In addition to posture and exercises, if you use a mouse, train your opposite hand so you can switch and give each hand/forearm a break. The first week of using the opposite hand was quite challenging for me. I became both physically and mentally tired quickly. But after the first week my accuracy and stamina was good enough for non-pixel perfect use.

[atxaqualion]

Good stuff. Immutability is really key to taking advantages of higher level programming languages that can parallel process your code without explicitly defining how the parallel processing occurs. This is why functional programming languages such as Scala, Clojure, etc. are gaining traction.

I've been using JavaScript for 20 years and several of your JavaScript-centric episodes teach me something new about how things work "under the hood". Thanks mpj.

[ahwaliazizi]

impressive... very smart, no keyboard strok sound, no nasty backgroud sounds, theroy plus practical, deep knowledge so deep explaination ....amazing video !

[afitnessca]

Hey just wanted to say thanks. I am a 3 years into Java development, was trained in one of the software development bootcamps and learned ruby. As JavaScript is taking over the world my knowledge about it was very basic, and your tutorials makes me interested to apply more of these principles. I do find your videos very engaging, very informative, clear and concise. Thank you.

[vacprokop]

I have learned two universal principles so far: minimize scope and don't reassign a variable. Well done with this episode!

[stevenwilson]

I'm not even a JS programmer, but your show is so well done I look forward to it and watch it every week! Thank you!

[ujleflc]

Great video sir! in terms of ergonomics: i used to experience what you described on a daily basis previously.
What fixed it for my was: Have a chair which has a good straight sit mode (not hanging back nor too forwards) and make sure that your chair has armrests where your elbow can rest at height of about 2/3cm lower than your desk height.
Also what is essential is using a mouse that suits your hand. It would shock you to know how many people use too small mice.
A nice long mouse ergonomics wise is the Razer Deathadder.

Again thanks for making these awsome video's for new aspiring JS devs and i hope your arm is okay again by now!

[davidbrewitz]

I trained my left hand to be as efficient as my right hand using the mouse. It was annoying for the first week or two but you will appreciate being able too switch back and forth when one gets too painful. Its always good to have a backup.
Thanks for the awesome vid's by the way!

[erickvoodoo]

Thank you! I've been waited for next lesson about ES6 features and now I have it!

[rdagger]

I had bad wrist pains from long days at the computer. I cured it by adding dumbbell wrist curls and reverse wrist curls to my workouts. 4 sets of 12 reps with light weights, 3 times a week. I also use gel keyboard and mouse wrist rests to try to keep my wrists in the same plane as my forearm. I’ve been wrist pain free for several years. Now would be a good time to also add some preventive shoulder exercises because that is another very bad consequence of too much desk work.

[jamesmcginn]

"It's so nice for something to be immutable." Great explanation. I loved the dishwasher analogy. Thank you!

[patrickbarnes]

Just discovered you today and can't stop watching. Great content and humor! Concerning arm pain: I had this and it was due to clicking on mouse buttons. Makes sense that extending a finger and mashing a button hundreds of times a day would cause RSI. Problem went away quickly and has stayed away for years when I replaced the mouse with, first, a Wacom tablet and later a magic track pad with tap to click enabled.