Creating a blockchain with Javascript (Blockchain, part 1)

Learn how to write your own Blockchain with JavaScript. In this video I'll show you what is behind a blockchain by using simple code. It's not a complete implementation, but enough to understand how blockchains work and how they guarantee that blocks can never be changed.
After creating our blockchain we'll try and tamper with it. This will demonstrate a blockchains ability to detect fraud.
Next video (implementing proof-of-work):
• Implementing Proof-of-...
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#blockchain #javascript #coding #crypto #nodejs #simplyexplained

[@tauwheed3055]

I do not understand anything about coding, but the way this mysterious gentleman stated everything, I was completely hooked up seconds by seconds till the end. I guess some peoples do have some extraordinary quality of teaching. Thanks Savjee

[@ViralVeediuh]

Tauw heed it’s that you actually care about learning about blockchain. Trying watching a video on programming a microwave keypad. Much less interesting lol

[@BigDaddyDax]

Agreed!!

[@BigDaddyDax]

@@ViralVeediuh true

[@aayushpratapsingh5860]

Same here

[@pajamasoverpeople4412]

SAME.

[@vegn_brit5176]

Great video. I'm a programmer so this made a lot more sense to me than watching someone try to describe how the blockchain works in a spoken presentation!

[@prabhusingh7481]

Demystified this for me, finally! Thank you so much for making these concepts so tangible.

[@lucysluckyday]

My gosh, in terms of covering the basic fundamentals this is an amazing intro!

[@FacundoTroitero]

After +1 year of courses, projects documentation and tutorials I could finally understand how Javascript classes work thanks to this video. Thanks!

[@owenparker6651]

Savjee, I have finally been compelled to subscribe to a youtube channel. As an 'old dog' programmer, you have got me moving on blockchains more than the dozens and dozens and dozens of articles I have read. For a 'show me' programmer, this is just what the doctor ordered and I thank you for taking to the time to share your knowledge and for doing such an easily understood walk-through. Well done young man...

[@simplyexplained]

Thanks a lot! Reading your comments made my day!

[@jessss7792]

Very well done video. Steady pace, clear code, and an engaging voice. The blockchain just became a whole lot less intimidating and mysterious, so thank you.

[@Procyon58]

So much information fit in this 15 minutes and this finally made blockchain click in my head. Thank you for this!

[@niklavr]

Yes! Really helpful video! Thanks!

[@luckyadeloye3452]

Especially the explanation of difficulty and nonce.

[@seanrosen9855]

Exactly! Over all those explanations online which doesn't provide any example, I can finally understand the base concept of a blackchain after watching this video, thank you soooo much. Autosubs

[@nitinchaudhary7686]

How can i make zsh in terminal

[@stanicng]

Same here. I think we belong to developer world. Simple words can't make us understand until read the programing logic. Hehe.

[@blackswan7568]

For my internship, I was recently requested to do a simple web3-based project. This is what I've decided to use. Thanks for this project and for being a great teacher😁

[@TheStoriesProductions]

"Simply Explained" indeed ! Amazing, cleared a lot of concepts.

[@saxenaabhi]

Oh man, after watching heaps of videos on bitcoin, etherium and block chain. This is the first time I really got my head around only because we think in terms of code. Love you for that.

[@joeysipos]

yeah, seriously. All these explanation videos make no sense. But looking at how the code actually works make perfect sense haha.

[@astrarai-thesobercoder]

Same here 👨🏽‍💻

[@jasonpatel6562]

@@joeysipos if(currentBlock.hash !== currentBlock.calculateHash()){} TypeError: currentBlock.calculateHash is not a function : thats the error I got, not sure why it is function

[@clementbourcart785]

Love this! Thanks so much for making this tutorial, really helps a non-techie like me get under the hood of blockchain!

[@Ricardoromero4444]

Damn bro, that light theme doesn't hurt your eyes?

[@snikkerrr286]

😂😂😂😂

[@hansphung]

and the bracket on the same line with the parentheses and no space, ew

[@slavento]

Try working in very light room...it's common to work with light theme in that case, and with dark theme in darker rooms...

[@rangarajann1781]

@@slavento yeah using dark theme in bright light environment is not good. Dark theme is perfect for only dark environments. And light theme is good for brighter environments

[@jorgepvenegas]

Does anybody know which theme is he using?

[@sicko_drops]

great video. subscribed!

[@dukewellington5222]

Explaining it in code makes blockchain technology so much easier to understand. Thank you for this! Great job!

[@AkhilPrabhakaran]

Wonder I didn't come across your page months ago. Not just for this particular video but the quality and the clarity in all your videos are amazing. Huge fan!!

[@slapassdevil]

First! Also great videos man, thank you so much!

[@simplyexplained]

+Anthony Dutra Glad you like them! (And wow that was fast!)

[@classborn]

Subbed , you brought tears to my eyes.

[@kukuster]

exactly. That's why dark theme *is better*

[@nestoreduardoirahetamazari9409]

Great! I was learning blockchain but with a traditional school teaching for weeks and I didn’t understand nothing but with your videos I completely hooked up great and very simple way to learn thanks and appreciate to share your knowledge ❤

[@FreedomForKashmir]

I swear, this is the video finally where I really understood the concept of Blockchain. I have watched many videos but was getting just repetitive things time and time again. Thank You very much. I have like and subscribed to you channel.

[@vasanthkumar2190]

This looks similar to linked lists in Data Structure with added security!

[@cazino4]

Great observation!! It is similar to a Singular Linked List data structure With one massively important improvement namely: O(1) (i.e constant time access) to all blocks in the chain, via the top-level array.

[@Mailmartinviljoen]

May i nitpick? The focus is on integrity which make it inherintly secure 😁

[@frumpledpigskin]

i was thinking the same thing

[@SatyamGupta-gc9sq]

@@cazino4 yup it's linked list but not singly linked list, it's doubly linked list as it stores the adress of the previous block too.

[@cazino4]

@@SatyamGupta-gc9sq Nope, you're INCORRECT!! Please revisit the source code - it is quite clear. The presented Block Chain data structure has more commonalities with a SINGULARLY Linked List, NOT a doubly linked list as you have attempted to suggest. Whilst I agree that the structure does indeed store reference to the previous node (i.e its parent) it DOES NOT *DIRECTLY* store reference to the NEXT node. Thus it's essentially a singularly linked list in reverse.... But STILL a singularly linked list nonetheless. Source: myself lol. I've actually built these types of core data structures (i.e Singularly/Doubly linked lists, Binary Search Trees, Balanced Binary Search Trees,Tries,etc) from scratch in numerous languages and have a deep understanding of matters pertaining to their. respective implementations,trade-offs, time-space complexity,etc

[@hashmoody]

Really great, that sparked a great idea in my mind! :) (y)

[@joyhearrington8503]

You are a great teacher, Mr. X! Thankfully, I do not have to write this code but I needed to understand blockchain for my graduate class. This video finally made it all click! (I watched your other one before this too and that was helpful as well.) Keep up the great work and thank you for sharing it for free!

[@mauriziomaisto2874]

Great tutorial, thank you. I was "playing" with your code and i've just discovered that changing the "Genesis block" (block 0) attributes is possible (the chain stays valid). This is due to the "isChainValid()" method; as you can see, the method has a "for(var i = 1; i < this.chain.length; i++){ [...]" which starts from "i = 1". This means that no controls are applied to the first block (data can be changed without any problem). A simple work-around is to change the "for([..])" loop (make it starts from "i=0" and check the previous block only "if(i>0)"). Thanks for your time and knowledge

[@mi13estrellas]

would implementing some of those other features such as "proof of work/ stake", check of funds, ability to prevent tampering of data / rollback function be possible to demonstrate in another video? It would be greatly appreciated.

[@daezohn8662]

Not to mention P2P network consensus and transaction broadcasting. I sometimes think writing your own blockchain is just as ambitions as writing your own OS. Maybe it is just easier to take to bitcoin code and adapt it to your needs.

[@utopialabsvideos9408]

@Sophie, do you want a complete implementation? Just read the source code for Bitcoin or Ethereum...

[@lucysluckyday]

Yeah the actual source code is the best option when you want to understand the more complicated aspects of merkle trees, nonces, unconfirmed transactions, and memory pools. But this is an extremely good generic intro on the fundamentals !!!

[@SwadeshiBakchod]

13:02 Blockchain is like "Mr.Stark...I dont feel so good..."

[@luizdrumonddeandrade7065]

Just amazing how you have explained this topic in a really easy way. Congratulations!!!

[@ulfkarlsson272]

Thanks, I had the theoretical understanding of what a blockchain was before, but seeing it explained this way makes everything much clearer.

[@AmitYadav786]

Awesome intro, I think you should make this a series so that people can make their own full blockchain using your details. When is the next video coming??

[@simplyexplained]

+Amit Yadav Great idea! Next stop would be to discover smart contracts. Definitely will work on that in the future. But first I need to finish another course ;)

[@simplyexplained]

+Amit Yadav Great idea! Next stop would be to discover smart contracts. Definitely will work on that in the future. But first I need to finish another course ;)

[@nitinchaudhary7686]

Amit Yadav how can i make zsh in terminal?

[@stanfordnwosu424]

Simply Explained - Savjee Heyy any luck with making those blockchain courses

[@JavaScriptRoom]

Hey! Thanks for the great content! One question: why didn't you generate block's index and timestamp on a fly in the constructor? Is there any reason for passing them on instance initiation?

[@oderingpush8054]

hello, has this improved your knowledge of java and blockchain? have you made any progress on creating a blockchain? i would like to talk with somebody who might be able to help me script a source of a new blockchain

[@AhmadNasikun]

Thanks for the great tutorial. There are lots of videos describing how blockchain works, but only a few that give some technical example(s). Among those few, this video stands out really well. For those who are new to blockchain (e.g. me), this video is really enlightening.

[@CourtneyZinckgraf]

I know nothing about coding, but this example really made me understand what's happening with blockchains - thank you!

[@jekabolt]

it's will be great if you create a. video about smart contracts

[@simplyexplained]

That's a nice idea! I'll definitely consider that!

[@python_tutorials6519]

yeah pls do that and can u include dates in smart contracts for tokens to be distributed only during that time?

[@simplyexplained]

+Python_Tutorials Great idea! I'll think about how to implement that :)

[@python_tutorials6519]

great,thanks a lot and we would love to wait for that video

[@arhabersham]

WORD!

[@calvinlin6670]

It's a great explanation video of Blockchain. Can you tell what IDE you are using 0.0 Cuz i really like the UI , thanks

[@RoadToFuture007]

Hafrn The Grey white edition ;)

[@MistaT44]

Press ctrl k + ctrl t, and select the quiet light theme :)

[@adriancelis9691]

This is amazing. I dont even do Javascript (just php) and i understand what you're saying. Great vid.

[@SubhrajitSadhukhan]

Thanks man. This really helps understand the concept without going into too much or too little details. Exactly what I was looking for.

[@albertkeller3773]

How can I download the library on Windows? Because on windows the terminal is working with powershell

[@AbdulAhad-ni4hq]

same problem here did u solved ?

[@safaelboukhari5431]

@@AbdulAhad-ni4hq same probleme :(

[@alvarovalenzuela7389]

use bash instead :)

[@eoussama]

You need npm installed.

[@robincard1548]

If you're really serious, I would switch your desktop from Windows to Ubuntu Desktop (free) or run Ubuntu in VirtualBox (free). Windows and Node/Javascript don't play well yet, there are still lots of problems with file names and stuff. The windows guys I work with are always having problems, the people on the *Nix/Mac system dont have these problems ever. I'm not saying Linux/Mac is better than Windows, just saying that for now JavaScript is better on Linux/Mac. They my fix it soon.

[@mattyzacharia]

Great video. Congratulations. I have a question though, in the example, I tried to tamper data and did recalculation of current hash and assigned to existing hash. I got output as true. We are not tampering anything with previous block hash. Basically I have not understand the check on current block hash with the previous block hash as for me it always return true. Also if I carefully watch video , when you do a tampering and set current hash. It gives output as false. However if I examine your console which is on this video, both previous hash and current hash seems to be identical. Then how does it return false? Thanks Matty

[@dukewellington5222]

Did you put the return true statement in the body of the for loop?

[@mzaki8503]

I am having the same exact problem now. Did you manage to solve it?

[@Chris-oe4pj]

when isChainValid loops and checks the block that is right after the one you changed, its previous hash will not match that preceding block's new hash that you had calculated

[@sreelalts1892]

Amazingly explained! I really didn't know anything about Blockchain. After watching this video, I was like "wow, this guy is amazing!". You did it so nice Savjee! Thanks a lot!

[@mstafadev6729]

I've watched too many videos to understand what a blockchain is and none of them seemed to help, but this video clears things up in my head about blockchain, Thanks

[@rkj541]

Greatly explained the concept in a short video, great job!!

[@joshuacoll.6100]

BRUH thank you so much!! I needed a simple implementable example with the core concepts intact!! Thanks again dude you are the best!! :D

[@laude94wuo]

Clear coding style makes a complex concept to be so easy that everyone can understand! Amazing...!

[@fernandofradegrada]

Very clean explanation, and also very clean english for those who doesn't speak english natively. Thanks!

[@simplyexplained]

I'm not a native speaker myself, so I have to keep things simple ;)

[@jagodiving]

there were a few genious on algorithm n coding, but i think you one the best amid them....simple n clear

[@ib6435]

Watching this in 2020 and its broadens my programming knowledge. Thanks!

[@lovebajpai5288]

Fantastic!!! What an explanation! it just makes you understand the whole thing in one video!

[@fastindemand6074]

This video was simple and informative. thank you.

[@MadhavanR]

Noticed this video on my recommendation and in 15mins understood the basics of blockchain… most importantly the simple and powerful sample you showed👍🏻👍🏻👍🏻

[@VincentNoben]

This explanation is so solid! Like others said in the comments, this is what made me get it. I sortoff knew but this made the click and will make it much easier for me to explain it myself in the future. Thanks!

[@tharhtoo2149]

Thank you so much, Sir. You just make the whole concept of blockchain sys clear for me in just under 15 mins.

[@Mailmartinviljoen]

Clarity by far the best tutorial i have ever seen

[@Superb_virg]

Extremely simple and well explained amazing.

[@nitinnimkar1654]

Thanks Brother....you have pushed me in right direction. I was reading, watching many videos on Block Chain, but your Javascript example cleared lot of ideas. Thanks again. May I tell you, I have used many a times timestamp & date to create a unique ID for various databases. That concept has been expanded into something massive. Great work....

[@itshiraljain]

You simply explained and I simply subscribed. This is what I was searching for as I don't knew any implementation of blockchain. thankyou

[@funmeister]

Absolutely love this video. Only regret is why I just found you now. Subscribed!

[@breal1460]

Thank you for sharing this. Today I decided to learn about blockchain. I hope I can learn enough to produce something to help make our world a better place.

[@bhag1]

This is great. Simple and crisp. Thanks!

[@kundanjangir3729]

Very Good explanation, You have earned that subscribe Amazing work sir I was looking for a new tech to learn and with your starting explanation I will go for Blockchain. Thanks

[@marcelosabadini]

Best 14 min of the year!! tks a lot!

[@imadsaidi5909]

Thank you Savjee. Great video and well explained too.

[@I_love_mbs]

Thanks a lot. Very helpful. Good video to start with when learning blockchain technology, and narration is good too. The BASICS seem SIMPLE; build a constructor and hash it then, link each instance like nodes, loop through the nodes, do some logical statements for validations, have the chain stored on local computers, and there you have it. I think. Please let me know.

[@sanatanmeaning]

Thank you Savjee for free and *high quality* knowledge

[@thejmcexperience8755]

Thanks for the series. This has helped me understand blockchain.

[@gazisalahuddin8907]

Great, you understand concepts through building them. Thanks, man.

[@mubafaw]

Wow! This explanation demystified the whole concept of blockchain . Thanks 😊👍

[@mauriciogambini]

simple, objective and complete ! Thanks :)

[@germandiagogomez]

Very nice introduction. Perfectly explained concepts in a compressed timespan.

[@amnest1ac]

This is so easy. For all the noise this "technology" has made. I am impressed how fundamentally basic is the idea itself.

[@Bagga4u]

Thank you for clearly and efficiently explaining the concept of block chain. Now it makes sense :)

[@kkmetcom]

can't thank you enough, this is great, might be my entrance to this world, thank you Savjee

[@richaagrawal4416]

for the first time in life i have watched the whole info stuffed youtube video in one go. keep it up man!!

[@md.jayeenbinalam.6194]

The best beginner level blockchain tutorial.

[@broonzy2006]

wow! great video... I'm a low level dev and by watching the last 2 videos, really got the concept and quick application. Cool!

[@shivaskanthan6144]

Excellent 11/10. Detailed, concise and easy to understand.

[@stevenzhang8620]

Very well explained blockchain in simple javascript code! Thanks a loooot!

[@WhatIsThisAllAbout]

thanks man...I was wondering how this works in code & thats what you explained so clearly.

[@prithvidheer6893]

Loved the explanation. You got a nice way of teaching.......Thanks :)

[@zhangbruce4815]

Best block chain explanation video so far I've seen

[@Frank2tek]

Best and simple way to understand the core concept of blockchain . Nice job ...

[@s2r2420]

Great Video. Thanks for this informative short video

[@kinderdll3246]

Congrats !! Great video and presentation of basic blockchain concepts

[@bobsmithy3103]

Wow, amazing job man. I've only covered the basics of Javascript yet your explanation of every part of your code made everything so clear. Your name really does suit the quality of your content. Thanks a ton man!

[@simplyexplained]

Thanks for the kind words! Makes my day ;)

[@lindadehaan]

I liked this very much! Thanks for the demo.

[@mizlagunesvary5077]

Wow.. Thanks, Sanjeev for this video. I`ve been searching for something to enlighten my brain with what`s actually Blockchain is. Finally, you did it... Thanks man

[@dzianisdashkevich1848]

great videos, and this one is also nice and clear! thanks for it. Wish you will continue to implement more advance and complicated things from this area

[@bawbee27]

This is an excellent tutorial. Thank you!

[@Shortly8908]

Thanks bro. I imagine blockchain works like magic until i watched your video.

[@torbilan6292]

Thanks , such a clean code and clear speech. Benefited a lot !

[@arnab1prince]

Amazing.. Really liked the way you explained! Big thumbs up

[@Katie-zq9ib]

Thanks a lot for this simple walk-through of how blockchain works! The example was simple and easy to follow 👍🏽

[@jacob_dmn]

so so helpful, I can't believe all that happened in 15min. Love it. Please keep it up

[@desertfox9613]

One of the best explanations on the net!

[@tactteam00]

You gave an efficient and easy to understand intro to blockchain development. Subscribed

[@simplyexplained]

Glad you liked it!

[@johnsonabiaeme9018]

Simply cool and straight forward. Thanks man

[@007KrausBean]

Really good video. This is a great way to present Blockchain to a visual learner like me.

[@0117shaowei]

Love this video! Amazing explanation :)

[@chunkin9799]

Clutch video. Excellent explanation of block chain. So much simpler of a concept than when you just hear it explained.

[@dj_averion]

Easy explained and good to follow. Thanks!

[@claudiograsso]

Excellent!!!! Thanks a lot for such a clear explanation.