# sign

Signs a Bitcoin transaction.

# Type

;(
  tx: NakamotoJS.Transaction,
  opts: {
    inputIndex?: number
    sighashType?: number
    inputScript?: Buffer
  },
) => Promise<void>

# Parameters

# `tx`

A Bitcoin transaction, possibly partially signed.

# `opts`

The opts object can have the following properties:

Key	Type	Description
inputIndex	number	The input index to be signed
sighashType	number	A valid sighash type number
inputScript	Buffer	A buffer encoding the signature

# Return Value

The function returns void.

# Description

By default, the sign function will make a best effort to sign all inputs, but will not throw an error if the signature cannot be added due to hash mismatch.

This is useful in the case of partially signed transactions, where a user can encode an expression, sign with the user private key and send the generated partially signed transaction to another user. Then, the receiver can sign other inputs.

# Example

import { Computer, Contract } from '@bitcoin-computer/lib'
import { chain, network, url } from '../../utils'

// A smart contract
class C extends Contract {}

describe('sign', () => {
  it('Should sign a transaction', async () => {
    // Create and fund wallet
    const computer = new Computer({ chain, network, url })
    await computer.faucet(1e8)

    // Build transaction
    const { tx } = await computer.encode({
      exp: `${C} new C()`,
      sign: false,
    })

    // Sign transaction
    await computer.sign(tx)

    // Broadcast to see it it worked
    await computer.broadcast(tx)
  })
})

Sources