This is a simple Bitcoin testnet wallet with the purpose of teaching new users to Bitcoin how to program for Bitcoin with JavaScript. It assumes that you have some programming experience - JavaScript experience would be even better.

It's assumed that you have Node.js and git git installed.

Understand the following...

At the moment, the programs are take advantage of Unix shell scripting. This will change eventually, but to get the programs ot run on Windows, you'll need to remove the first line (#!/usr/bin/env node) in all files in bin/. Then you'll need to run the script with the actual node binary. e.g.

instead of

bin/addr-balance.js

you'd do

node bin/addr-balance.js

It uses the Bitcoin test network. So actual bitcoins aren't necessary.

You can use the Coinbolt Catshop to test buying things with Bitcoin. It is an open source as well: https://github.com/coinbolt/catshop

These scripts all use https://helloblock.io to communicate with the Bitcoin network. You should use it too.

Shallow clone the repository. This will include all dependencies.

git clone [email protected]:coinbolt/simple-wallet.git --depth 1

Navigate to simple-wallet directory.

This will create a new wallet with just one and only one address. This is a bad idea in practice for two reasons:

1. your public key is exposed and could potentially lend itself to an attack (unlikely, but still possible)
2. sacrifice of privacy

But for the sake of learning, it simplifies things.

bin/addr-new.js

You'll see an output that resembles:

  wallet created with address:

    mvfeyJyxtX4CZEfpxp8tYZ4BRtzaTPbXbb

A new wallet file was created. It exists at simple-wallet/wallet.json.

To really understand what's going on, you should read this: http://procbits.com/2013/08/27/generating-a-bitcoin-address-with-javascript The aforementioned tutorial uses an older version of bitcoinjs-lib but it's included on the page so that you can open a chrome or firefox console and follow along.

bin/addr-balance.js

output:

  balance for mvfeyJyxtX4CZEfpxp8tYZ4BRtzaTPbXbb

    0.00 BITS

You'll want to add some funds. But how? Use either:

1. http://faucet.xeno-genesis.com/
2. http://tpfaucet.appspot.com/

Paste in your address into one of those sites and deposit some funds. Then check your balance:

bin/addr-balance.js

output:

  balance for mvfeyJyxtX4CZEfpxp8tYZ4BRtzaTPbXbb

    100,000.00 BITS

Bitcoin transactions are simply a data structure that links inputs (from previous transactions) and outputs which are scripts that should do something. In most cases, said scripts involve transfering of ownership of the bitcoin.

To create a transaction, you must get what's referred to as the unspent outputs associated with your address:

bin/unspents.js

output:

[
  {
    "confirmations": 4,
    "blockHeight": 309400,
    "txHash": "c65222345cb941d76e29ecf8a44c35be0f6a3e4396f008ca3ace978e4e19eb20",
    "index": 0,
    "scriptPubKey": "76a914a62f2b75f54f9f65c276c6dfacb365726f6dd42188ac",
    "type": "pubkeyhash",
    "value": 10000000,
    "hash160": "a62f2b75f54f9f65c276c6dfacb365726f6dd421",
    "address": "mvfeyJyxtX4CZEfpxp8tYZ4BRtzaTPbXbb"
  }
]

This output describes the input transactions to this current address.

Then you must create and sign the transaction (you need to pipe in the output from addr-unspents):

bin/addr-unspents.js | bin/tx-make.js mmncSwJoFvTe1WZVM4QQtTguosepHvtdGG 2500

the program tx-make.js requires that the first mandatory command line argument be the destination address and the second optional argument be the amount in bits to send. If no amount is specified, the entire wallet balance is sent. Since we're dealing with test coins, it's not a big deal.

output:

010000000120eb194e8e97ce3aca08f096433e6a0fbe354ca4f8ec296ed741b95c342252c6000000006a473044022073fdaa1b45bc24a92da95ff28515a970888fbfc8924f3fe949a6fc2ed8fe3637022005f8305f28ab0834eaea787c0d9266156a619907482154bfff3a4b8c9c597971012102006f39d9a3938e9e151e0b5ca72226113d9d5c912c1667f5d258e187171d6f5effffffff0290d00300000000001976a91444c6d7c083cb9bf85c206f2fe2a6093af8a2b50b88ace09e9400000000001976a914a62f2b75f54f9f65c276c6dfacb365726f6dd42188ac00000000

This output is the hex encoded version of the transaction. You could copy and paste it to manually submit it to either: https://test.helloblock.io/propagate or http://tbtc.blockr.io/tx/push

or, you can use tx-send.js:

bin/addr-unspents.js | bin/tx-make.js mmncSwJoFvTe1WZVM4QQtTguosepHvtdGG 2500 | bin/tx-send.js    

output:

  success!

    tx id: ef92d8f909319780e0bb347c4be2ba34dbbd5e751ceaca1a453932103aa09435

You can then use this transaction id to find out more information using other APIs or the API explorers e.g. http://tbtc.blockr.io/tx/info/ef92d8f909319780e0bb347c4be2ba34dbbd5e751ceaca1a453932103aa09435 or https://test.helloblock.io/transactions/ef92d8f909319780e0bb347c4be2ba34dbbd5e751ceaca1a453932103aa09435

Now check your balance again:

bin/addr-balance.js

  balance for mvfeyJyxtX4CZEfpxp8tYZ4BRtzaTPbXbb

    97,400.00 BITS

(note 100 BITS were taken as a fee for miners)

You could skip all of the piping and just use the send.js program as well:

bin/send.js mmncSwJoFvTe1WZVM4QQtTguosepHvtdGG 2500

Additional resources on transactions:

• https://curiosity-driven.org/low-level-bitcoin (uses JavaScript, excellent tutorial)
• http://www.righto.com/2014/02/bitcoins-hard-way-using-raw-bitcoin.html
• http://www.michaelnielsen.org/ddi/how-the-bitcoin-protocol-actually-works/ (this actually on mining, but worth reading)