Compute transaction hash locally?

Question

The usual workflow to submit an EVM transaction seems to be:

1. Call the send(Raw)Transaction RPC method.
2. Use the returned transaction hash to query the status of your transaction.

My question is, is it possible to precompute the transaction hash before submitting the transaction to the node? I believe this would simplify the transaction tracking as it would allow me to start listening for the transaction right from the start. If instead I have to wait for the hash first, then once I receive the hash I first need to check the history whether the transaction has been mined already, and only then can I start looking for the transaction in new blocks.

Answer 1

For web3 there's web3.eth.signTransaction returns the hash of the transaction in the 'hash' field.

{
    raw: '0xf86c...',
    tx: {
        nonce: '0x0',
        ...
        hash: '0xda3be87732110de6c1354c83770aae630ede9ac308d9f7b399ecfba23d923384'
    }
}

Similarly web3.eth.sendTransaction returns a PromiEvent. This object provide several events that you can listen to, one of them is transactionHash

// using the event emitter 
web3.eth.sendTransaction({
    from: '0xde0B295669a9FD93d5F28D9Ec85E40f4cb697BAe',
    to: '0x11f4d0A3c12e86B4b5F39B213F7E19D048276DAe',
    value: '1000000000000000' })
})
.on('transactionHash', function(hash) {
    // hash is available
})
.on('receipt', function(receipt){
    // tx was mined
})