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Learn Blockchain Programming with JavaScript
Learn Blockchain Programming with JavaScript

Learn Blockchain Programming with JavaScript: Build your very own Blockchain and decentralized network with JavaScript and Node.js

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Learn Blockchain Programming with JavaScript

Building a Blockchain

In the previous chapter, we learned about what a blockchain is and how it functions. In addition, we learned how to set up a project to build our blockchain. In this chapter, you will begin building the blockchain and all of its functionalities. First, let's create the blockchain data structure using a constructor function, and then we'll add a lot of different types of functionalities to our blockchain by adding different methods to its prototype.

We're then going to give the blockchain certain functionalities, such as creating new blocks and transactions, as well as the ability to hash data and blocks. We'll also give it the ability to do a proof of work and many other functionalities that a blockchain should be able to do. We'll then make sure that the blockchain is fully functional by testing the added functionalities as we progress...

Before we get building...

Before we get into building the blockchain, there are two crucial concepts that we need to familiarize ourselves with. These important concepts are as follows:

  • The JavaScript constructor function
  • The prototype object

An explanation of the JavaScript constructor function

Becoming familiar with the constructor function is important as we'll be using it to build our blockchain data structure. By now, you must be wondering what a constructor function is and what it actually does.

A constructor function is simply a function that creates an object class and allows you to easily create multiple instances of that particular class. What this actually means is that the constructor function allows you...

Blockchain constructor function

Let's get started with building our blockchain data structure. We'll start by opening all of the files that we have in our blockchain directory by using the Sublime editor. If you are comfortable using any other editor, you can use that too. Open our entire blockchain directory in whichever editor you prefer.

We'll be building our entire blockchain data structure in the dev/blockchain.js file that we created in Chapter 1, Setting up the Project. Let's build this blockchain data structure by using a constructor function that we learned about in the previous section. So, let's begin:

For the constructor by type the following:

function Blockchain () {
}

For now, the Blockchain () function is not going to take any parameters.

Next, inside of our constructor function, we are going to add the following terms:

function Blockchain...

Building the createNewBlock method

Let's continue with building our blockchain data structure. After defining our constructor function in the previous section, the next thing that we want to do with our constructor function is to place a method in our Blockchain function. This method that we are going to create will be called createNewBlock. As its name suggests, this method will create a new block for us. Let's follow the below mentioned steps to build the method:

  1. The createNewBlock method will be defined as follows:
Blockchain.prototype.createNewBlock = function () { 

}
  1. Now we've got this createNewBlock method on our blockchain prototype object. This method will take the three parameters, as highlighted in the following line of code:
Blockchain.prototype.createNewBlock = function (nonce, previousBlockHash, hash) { 

}

We'll learn in depth about these...

Building the getLastBlock method

Now, the next method that we are going to add to our Blockchain constructor function will be the getLastBlock. This method will simply return the last block in our blockchain to us. Follow the below mentioned steps to build the method:

  1. Go to our dev/blockchain.js file, and after our createNewBlock method, add the following:
Blockchain.prototype.getLastBlock = function () { 

}
  1. Inside of this getLastBlock method, we will type the following highlighted line of code:
Blockchain.prototype.getLastBlock = function () { 
return this.chain[this.chain.length - 1];

}

The [this.chain.length - 1]; in this preceding code defines the position of the block in the chain, which, in our case, is the previous block, therefore negated by 1. This method is simple and straightforward, and we'll use it in later chapters.

...

Creating the createNewTransaction method

The next method that we are going to add to our blockchain constructor function is called createNewTransaction. This method will create a new transaction for us. Let's follow the below mentioned steps to create the method:

  1. Start building up this method by adding the following line of code after our getLastBlock method:
Blockchain.prototype.createNewTransaction = function () {

}
  1. The function () will take three parameters, such as the following:
Blockchain.prototype.createNewTransaction = function (amount, sender, recipient) {

}

What these three parameters will do is as follows:

  • amount: This parameter will take in the amount of the transaction or how much is being sent in this transaction.
  • sender: This will take in the sender's address.
  • recipient: This will take in the recipient's address.
  1. The next thing that we want...

Hashing the data

The next method that we are going to look at and add into our blockchain data structure is called hashBlock. What this hashBlock method will do is take in a block from our blockchain and hash its data into a fixed length string. This hashed data will appear randomly.

In essence, what we're going to do is pass some blocks of data into this hash method, and in return we'll get a fixed-length string, which will simply be a hash data that is generated from the data that we passed in or from the block that we passed.

To add the hashBlock method to our blockchain data structure, type the following line of code after our createNewTransaction method:

Blockchain.prototype.hashBlock = function(blockdata) {

}

In our hashBlock method, blockdata will be the input data of our block from which we want to generate the hash.

So, how can we take a block or blocks...

What is a Proof of Work?

The next method that we are going to add to our blockchain data structure is the proofOfWork method. This method is very important and essential to the blockchain technology. It is because of this method that Bitcoin and many other blockchains are so secure.

Now, you must be getting curious about what a Proof of Work (PoW) actually is. Well, if we take a look at our blockchain, every blockchain is pretty much a list of blocks. Every single block has to be created and added to the chain. However, we don't just want any block to be created and added to the chain. We want to make sure that every block that is added to the chain is legitimate, has the correct transactions, and has the correct data inside of it. This is because if it doesn't have the correct transactions or the correct data, then people could fake how much Bitcoin they have and essentially...

Creating a genesis block

One more thing that we would have to add to our blockchain data structure is the genesis block. But what is a genesis block? Well, a genesis block is simply the first block in any blockchain.

To create our genesis block, we are going to use the createNewBlock method inside of the Blockchain() constructor function. Go to the dev/blockchain.js file, and inside of the blockchain constructor function type in the following highlighted lines of code:

function Blockchain () {
this.chain = [];
this.pendingTransactions =[];
this.createNewBlock();
}

As we observed in the previous section, the createNewBlock method takes in the value of a nonce, a previousBlockHash, and a hash as parameters. Since we're using the createNewBlock method over here to create the genesis block, we are not going to have any of those mentioned parameters. Instead...

Summary

In this chapter, we began by building the constructor function and then moved on to create some amazing methods such as createNewBlock, creatNewTransaction, getLastBlock, and so on. We then learned about the hashing method, SHA256 hashing, and created a method to generate a hash for our block data. We also learned what a proof of work is and how this works. In this chapter, you also got to learn how to test the various methods that we created and check whether they are working as expected. The methods that we have learned about in this chapter will be very useful for us in further chapters when we interact more with the blockchain.

If you want to get more familiar with the blockchain data structure, it is recommended that you open up the test.js file, test all of the methods, try to play around with those, observe how they work together, and have fun with it.

In the next...

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Key benefits

  • Develop bitcoin and blockchain-based cryptocurrencies using JavaScript
  • Create secure and high-performant blockchain networks
  • Build custom APIs and decentralized networks to host blockchain applications

Description

Learn Blockchain Programming with JavaScript begins by giving you a clear understanding of what blockchain technology is. You’ll then set up an environment to build your very own blockchain and you’ll add various functionalities to it. By adding functionalities to your blockchain such as the ability to mine new blocks, create transactions, and secure your blockchain through a proof-of-work you’ll gain an in-depth understanding of how blockchain technology functions. As you make your way through the chapters, you’ll learn how to build an API server to interact with your blockchain and how to host your blockchain on a decentralized network. You’ll also build a consensus algorithm and use it to verify data and keep the entire blockchain network synchronized. In the concluding chapters, you’ll finish building your blockchain prototype and gain a thorough understanding of why blockchain technology is so secure and valuable. By the end of this book, you'll understand how decentralized blockchain networks function and why decentralization is such an important feature for securing a blockchain.

Who is this book for?

Learn Blockchain Programming with JavaScript is for JavaScript developers who wish to learn about blockchain programming or build their own blockchain using JavaScript frameworks.

What you will learn

  • Gain an in-depth understanding of blockchain and the environment setup
  • Create your very own decentralized blockchain network from scratch
  • Build and test the various endpoints necessary to create a decentralized network
  • Learn about proof-of-work and the hashing algorithm used to secure data
  • Mine new blocks, create new transactions, and store the transactions in blocks
  • Explore the consensus algorithm and use it to synchronize the blockchain network
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Publication date : Nov 30, 2018
Length: 252 pages
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Language : English
ISBN-13 : 9781789618822
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Table of Contents

9 Chapters
Setting up the Project Chevron down icon Chevron up icon
Building a Blockchain Chevron down icon Chevron up icon
Accessing the Blockchain through an API Chevron down icon Chevron up icon
Creating a Decentralized Blockchain Network Chevron down icon Chevron up icon
Synchronizing the Network Chevron down icon Chevron up icon
Consensus Algorithms Chevron down icon Chevron up icon
Block Explorer Chevron down icon Chevron up icon
In conclusion... Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
(5 Ratings)
5 star 20%
4 star 40%
3 star 0%
2 star 0%
1 star 40%
Drusilla Charles Jan 03, 2022
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
I thought the description of how the blockchain works was very good, but if your going to teach someone about the programming aspect of it you need to make sure that your code is correct. So far, I have already found 3 errors in the code that he is showing in the book. What’s also confusing is that the code he has on GitHub is a bit different than what he is showing in the book. It took me over an hour to figure out that it wasn’t my fault it was his. As a programmer this is frustrating. :(
Amazon Verified review Amazon
Some Old Sage May 23, 2021
Full star icon Empty star icon Empty star icon Empty star icon Empty star icon 1
Really badly written and outdated javascript for 2021. Please read mastering bitcoin if you want to create a blockchain from scratch.
Amazon Verified review Amazon
Michael Mar 13, 2021
Full star icon Full star icon Full star icon Full star icon Full star icon 5
There is more than I was expecting to understand and it gently guides you through the making of a blockchain with the full comprehension of what you are doing. There is some error that in my opinion is what makes it even more fun. It can get pretty complicated for a beginner like me but if you are smart enought you will accept the challenge with a smile
Amazon Verified review Amazon
Colin Jun 26, 2019
Full star icon Empty star icon Empty star icon Empty star icon Empty star icon 1
Spent over an hour going in circles trying to get the promised code examples. Between Pakt Pub and Github, totally confusing and just didn't work. A pity, the book looks to be quite good.
Amazon Verified review Amazon
Konstantin Apr 24, 2019
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
I found this book overall good for getting up to speed on how the blockchain works. The only thing i didnt like about it was it doesn't go into digital signatures and signing transactions. I found that in other books. Apart from that i think its a great intro into beginning to understand how blockchains work. Best way to have a deeper understanding is to get your hands dirty in code. Recommended.
Amazon Verified review Amazon
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