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Mining rewards & transactions - Blockchain in Javascript (part 3) - YouTube
Channel: Simply Explained
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Hey everyone, my name is Xavier
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and in this video, we
will continue working
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on our little JavaScript
blockchain implementation.
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In the last two videos,
we created our blockchain
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and we secured it with the
proof-of-work algorithm.
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In this video, I'm going
to expand it a little bit
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and make it a simple cryptocurrency.
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To do that, we're going to do two things.
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Number one, we're gonna make it
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so that a block can contain
multiple transactions
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and number two, we're gonna
add rewards for miners.
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Now why would we wanna do that?
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Well when you start a cryptocurrency,
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you need to have virtual money or coins.
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And if you don't introduce
them somewhere in the system,
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no one can get any coins.
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Mining rewards,
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steadily introduce new
coins into the system.
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So, let's get going.
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Here I've opened up the source
code of the last two videos
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in Visual Studio Code,
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and I'm going to start by removing
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all of our test code near the bottom.
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We're gonna re-factor
a bunch of this stuff
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so this won't work anyway.
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I'm just gonna keep the
sajeevCoin instance.
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Next, I'm going to modify
the block class a bit,
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so that it supports multiple transactions.
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So instead of receiving a data field,
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I'm gonna say that it
receives transactions.
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That makes a little bit more sense.
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And we're gonna say this dot transactions
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equals transactions.
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I'm also going to remove the
index argument right here
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because I've added that in the first video
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but it's actually not
useful in a blockchain.
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The order of blocks
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is determined by their
position in the area,
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and not by the index
that we can pass here.
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So when I remove index from
the constructor block here,
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I also have to remove it from
our genesis block down here.
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All right, so this transaction argument
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will get an array of transactions.
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So, let's define what a
transaction looks like
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by creating a new class for a transaction.
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And I'm gonna say that
a transaction receives
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a fromAddress, a toAddress and an amount.
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This is pretty straightforward,
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a transaction always comes from someone,
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it goes to someone and it carries
a certain amount of coins.
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And then we're just going
to assign each of these.
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So fromAddress equals fromAddress,
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this dot toAdress equals toAddress,
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this dot amount equals amount.
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With that out the way,
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we can start working on
our main blockchain class.
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There are a few things
that we have to do here.
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We have to add a mining reward.
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We need a place to store
pending transactions
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and we need a new method
to mine a new block
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for the pending transactions.
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Now you might ask yourself,
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what is this pending transaction
stuff and why do I need it?
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Well it's because we only create blocks
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on a specific interval.
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In Bitcoin's case, proof-of-work algorithm
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makes sure that there's
only one block created
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every 10 minutes.
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All the transactions that
are made in between blocks
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are temporarily stored in
this pendingTransactionsarray,
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so that they can be
included in the next block.
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So let's start with simple things first.
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I'm going to add a new property
to our blockchain class
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for our pendingTransactions.
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So I'm gonna call it this
dot pendingTransactions
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equals an empty array.
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And them I'm also going
to define a property
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that will control how much coins
the miners get as a reward.
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So I'm gonna say, this
dot miningReward equals,
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let's say, 100 coins if you
successfully mine a new block.
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I'm also going to reduce
the difficulty a bit
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so that it's just faster to test
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and then we can increase
again when we're done
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with our changes.
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Now that we have these changes,
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we're gonna work on our new mining method.
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So, this was our old mining method,
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the addBlock method, and
I'm gonna replace that
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by minePendingTransactions.
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Now minePendingTransactions,
this will receive an address.
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It will receive a miningRewarAddress.
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So when a miner calls this method
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it will pass along it's wallet address,
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and say, hey if I
successfully mined this block
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then send the reward to this address.
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Now, inside this method,
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we will start by creating a new block.
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So I'm gonna say let block
equals eight new Block.
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That requires a timestamp, so
I'm gonna say Date dot now.
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And then it requires some transaction,
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so we're gonna pass along
this dot pendingTransactions.
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We're gonna give it all of
our pending transactions
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that are currently
stored in our blockchain.
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Now in real world cryptocurrencies,
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like again, for instance, Bitcoin,
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adding all the
pendingTransactionsto a block
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isn't possible
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because there are way too
many pending transactions
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and because the block size
cannot increase one megabyte.
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So instead,
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miners get to choose which
transactions they include
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and which they don't.
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But we're not going to worry about this
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in our simple example,
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but just be aware that in reality,
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miners have to pick the transactions
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that they want to include.
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So after creating the
block, let's mine it.
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We're gonna say block dot minedBlock.
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And we're going to mine
it with the difficulty
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that is currently set
within our blockchain,
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right now it's two.
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And if that's done,
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we're gonna to log
something to the console.
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We're gonna say block successfully mined.
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And then we're going
to add it to our chain.
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So we're going to say this
dot chain dot push our block.
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And the last two things that we have to do
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is reset the pendingTransactions array
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and create a new transaction
to give the miner his reward.
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Now we can do this all in one go.
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We can just say that this
dot pendingTransactions
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equals an empty array,
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that will reset the pending transactions.
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But we can also just define
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an area which is one new element.
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So we can say new Transaction.
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The fromAddress, we're gonna say no.
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Because there isn't really a
fromAddress in a mine reward.
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It just comes out of this system,
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it's the algorithm that gives it to you.
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We're going to send it to
the miningRewardAddress,
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and how much coins are we going to send
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this dot miningRewards.
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Now, in the previous video,
some people pointed out,
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that they can change this code right here
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and give themselves more coins.
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And that's true, you really can do that.
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However, cryptocurrencies are powered
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by a peer-to-peer network and
other nodes in the network
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won't accept your
attempts of fooling them,
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and instead, they will just ignore you.
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So that's something
that I wanted to address
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from the previous videos.
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Now to continue,
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I'm also going to create a simple method
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called createTransaction.
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And this will receive a
transaction and all this will do
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is add this to the
pendingTransactions area.
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So we're going to push it on to that area.
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All right, now the final
thing that I'm going to do
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is I'm going to create a method,
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that checks the balance of an address.
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Many people thing that if you
send some bitcoins around,
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they actually move away
from your wallets balance
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to someone else's balance.
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But in reality, you don't
really have a balance.
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The transaction is just
stored on the blockchain,
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and if you ask for your balance,
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you have to go through
all the transactions
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that involve your address
and calculate it that way.
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So let's create a method for this.
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We gonna call this getBalanceOfAddress,
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and it will of course receive an address
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that we have to check its balance.
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We're going to say that
the balance starts at zero.
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And then we're going to
loop over all the blocks
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in our blockchain.
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So we're gonna say for constant
block of this dot chain.
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And because our blocks now
contain multiple transactions,
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we're going to say loop
over each transaction
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of the transactions in side this block.
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And then we have to write a bit of logic.
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If you are the fromAddress,
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that means that you've transferred money
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away from your wallet to someone else,
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so we have to reduce your balance.
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And if you are the toAddress,
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then you were the
receiver of a transaction
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and we have to increase your balance.
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So, we're going to say,
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if transaction fromAddress
equals the address
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that was given here and its address,
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then we're going to reduce your balance
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with the amount of the transaction.
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And if the toAddress equals
the address that you gave us,
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then we're going to increase your balance
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with the amount of the transaction.
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And when we're done
looping over all the blocks
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and all the transactions,
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we're just gonna return
the balance that you have.
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Alright, so now it's finally
time to test our code.
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I'm gonna scroll down
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and the first thing that I'm going to do
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is I'm going to create some transactions.
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I'm going to savjeeCoin
dot createTransaction.
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And we're going to make a
new Transaction object here.
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new Transaction.
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This has a fromAddress,
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I'm just going to give it
random strings here address one,
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to address two, and it
will send address two,
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let's say 100 coins.
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And then we're going to repeat that.
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And then we're going to say
that address two, for instance,
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gives address one 50 points
back, something like that.
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Now in reality address one and address two
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would be the public key
of someone's wallet.
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After we've created
these new transactions,
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they will be pending.
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They will be in the
pendingTransactions area.
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So we have to start the miner
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to actually create a block for them
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and store them on our blockchain.
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So I'm going to say console dot log,
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new line Starting the miner
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and then I'm going to say savjeeCoin
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dot minependingTransactions.
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And this method expects
a miningRewardAddress.
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In other words, it wants to know,
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where it should send the miningRewards to.
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So, I'm just going to
create another fake address.
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I'm gonna say Xavier's address.
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And after that is done,
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we're going to check my balance.
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So we're going to say console
log Balance of Xavier is,
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and then we're going
to say, savjeeCoin dot
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getBalanceOfAddress, xaviers address.
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All right, so let's save the file.
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And let's open the terminal and run it
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to see if it actually works.
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So I'm going to say
node source main dot js.
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And yeah, kind of works starting
the miner, mined the block,
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but then it says my balance still zero.
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Well, actually, that's correct,
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because in our mining
method if you remember,
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after a block has been mined,
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we create a new Transaction
to give you your miningReward,
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but that one is added to the
pendingTransactions array.
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So the miningReward will only be sent
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when the next block is mined.
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So, lets mine another one then.
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We say console dot log.
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Uh oops, kind of put that...
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Just copy it and put it there.
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So storing the miner again,
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and then we're gonna check my
balance again, right there.
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Save it.
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Run it again.
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And sure enough the second time,
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it increased our balance to 100.
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But in mining our second block,
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I also get a new reward
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which is again in the
pendingTransaction state
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and will again be included in
the next block that is mined.
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So, that concludes this video.
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We've transformed our block chain
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into a very simple cryptocurrency,
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where a block can contain
multiple transactions,
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and where miners get 100
coins in miningRewards.
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Now I want to point out that
this is a simplified version
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of a cryptocurrency and
it's for education purposes.
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Don't try to make your own
cryptocurrency with this.
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So that's it for now.
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If you haven't subscribed already,
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make sure you hit the subscribe button
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and also like this video.
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Thank you very much for watching,
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and I'll see you in the next video.
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