The Bitcoin Computer is a protocol for general purpose smart contracts on Bitcoin and Litecoin. It does not rely on a separate token, a separate blockchain or any trusted intermediaries. It works similar to ordinals, runes, and BRC20: you can build applications where users add metadata to a transaction to encode a smart contract interaction, such as minting a token. The software can parse the metadata back into smart contract data, for example which users owns how many tokens.
Our metadata format consists mostly of Javascript expressions to define the state updates. This makes it possible to build not just tokens but all applications directly on Bitcoin.
Create a file index.html and open it in your browser.
<html>
<head>
<script type="module">
// Import the library
import { Computer, Contract } from "https://unpkg.com/@bitcoin-computer/lib/dist/bc-lib.browser.min.mjs"
// Create a counter smart contract
class Counter extends Contract {
constructor() {
super({ n: 0 })
}
inc() {
this.n += 1
}
}
// Create a wallet and fund it
const computer = new Computer()
await computer.faucet(1e5)
// Mint a new on-chain object
const counter = await computer.new(Counter)
document.getElementById("count").innerHTML = counter.n
// Update the on-chain object
await counter.inc()
document.getElementById("count").innerHTML = counter.n
</script>
</head>
<body>
Count: <span id='count'>*</span>
</body>
</html>You should see Count: * at first, then Count: 0 and then Count: 1.
You need to have node.js installed. First install the Bitcoin Computer library.
npm install @bitcoin-computer/libThen create a file index.mjs containing a script that defines a Counter smart contract, mints a Counter object and the updates it.
import { Computer, Contract } from '@bitcoin-computer/lib'
// A smart contract
class Counter extends Contract {
constructor() {
super({ n: 0 })
}
inc() {
this.n += 1
}
}
// Create and fund a Bitcoin Computer wallet
const computer = new Computer()
await computer.faucet(1e5)
// Deploy a smart contract and create an object
const counter = await computer.new(Counter)
// Update the object
await counter.inc()
// Log the object
console.log(counter)Execute the script.
node index.mjsThe expected output is:
Counter {
n: 1,
_id: '656...024:0',
_rev: '90f...73f:0',
_root: '656...024:0',
_amount: 7860,
_owners: ['037...954']
}By default, an instance of the Computer class will connect to a Bitcoin Computer Node on regtest LTC at https://rltc.node.bitcoincomputer.io. You can run your own Bitcoin Computer node, see here for instructions.
To connect to your node, set the url parameter as shown below (see here for more configuration options). Make sure that the parameters chain and network match your node's configuration.
// Connect Bitcoin Computer wallet to a Bitcoin Computer node url
const computer = new Computer({
url: 'http://localhost:1031',
chain: 'LTC',
network: 'regtest'
})Creates a new client side wallet. You can pass a mnemonic as well a chain and network to the constructor as well as other optional parameters.
const computer = new Computer({
chain: 'LTC'
network: 'mainnet',
mnemonic: 'replace this seed'
addressType: 'p2wpkh',
path: "m/44'/0'/0'/0",
url: 'https://my-ltc-node.com',
satPerByte: 1
})Creates a smart object from a class and arguments to the constructor. An output of a Bitcoin transaction, that is inscribed with the constructor call, represents the smart object. The transaction id and output number is the id of the smart object.
A smart object can be updated through function calls. Function calls are also recorded in transactions. The new state of the object is represented by an output of this transaction that is inscribed with the function call. This output is the revision of a smart object.
class A extends Contract {
constructor(n) {
this.n = n
}
}
const a = await computer.new(A, [1])
expect(a).to.deep.equal({
n: 1,
_id: '667c...2357:0',
_rev: '667c...2357:0',
_root: '667c...2357:0',
_owners: [computer.getPublicKey()],
_amount: 5820
})Compute the value of a smart object given its revision.
const synced = await computer.sync(a._rev)
expect(synced).to.deep.equal(a)Deploys an ES6 module to Bitcoin. The module is inscribed in a Bitcoin transaction and the transaction id is the module specifier.
const revA = await computer.deploy(
`export class A {}`
)
const revB = await computer.deploy(`
import { A } from '${revA}'
export class B extends A {}
`)Loads an ES6 module from the blockchain given a modules specifier.
class A {}
const rev = await computer.deploy(`export ${A}`)
const { A: Loaded } = await computer.load(rev)
expect(Loaded).to.equal(A)Inputs a Javascript expression, possibly a module specifier, and possibly a "blockchain environment" that maps the (free) variables of the expression to utxos. The expression is evaluated in the scope of the module, substituting the (free) variables for the values computed for the respective utxo. A transaction is broadcast that spends the utxos, has one output for each object in the new state, and is inscribed with the expression, the module specifier and the blockchain environment. Returns the changed state after the evaluation and a transaction.
const { effect, tx } = await computer.encode({ exp: `${A} new A()` })Inputs a revision (transaction id and output number) and returns a Javascript expression, a module specifier, and a blockchain environment, if present.
const decoded = await computer.decode(tx)
expect(decoded).to.deep.equal({ exp: `${A} new A()` })Finds smart objects by module specifier or by owner. Also finds the latest revision of a smart object.
const revs = await computer.query({ publicKey })
expect(revs).eq(/* all revisions owned by publicKey */)Fund a client side library object on regtest. This is practical for testing.
await computer.faucet(0.001e8)Access the RPC interface of the Bitcoin node
await computer.rpcCall('getBlockchainInfo', '')- sign. Signs a Bitcoin transaction
- broadcast. Broadcasts a Bitcoin transaction
- send. Sends satoshis to an address
- getAddress. Returns the Bitcoin address of the computer wallet
- getBalance. Returns the balance in satoshi
Have a look at the docs.
If you have any questions, please let us know on Telegram, Twitter, or by email clemens@bitcoincomputer.io.
The Bitcoin Computer is, and will always be, free on testnet and regtest. This version of the Bitcoin Computer library is also free on mainnet, but we reserve the right to charge a small amount per transaction in future versions. Currently only miner fees apply.
We are in beta, so there is a possibility of bugs.
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