messageHash hash function

Question

In this example, by which algorithm is messageHash hashed by?

web3.eth.accounts.sign("Hello, world!", '0x0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef') { message: 'Hello, world!', messageHash: '0xb453bd4e271eed985cbab8231da609c4ce0a9cf1f763b6c1594e76315510e0f1', v: '0x1b', r: '0x3bc843a917d6c19c487c1d0c660cdd61389ce2a7651ee3171bcc212ffddca164', s: '0x193f1f2e06f7ed8f9fbf2254232d99848a8102b552032b68a5507b4d81492f0f', signature: '0x3bc843a917d6c19c487c1d0c660cdd61389ce2a7651ee3171bcc212ffddca164193f1f2e06f7ed8f9fbf2254232d99848a8102b552032b68a5507b4d81492f0f1b' }

Answer 1

It is explained in web3 documentation for web3.eth.accounts.hashMessage(message)

Hashes the given message to be passed web3.eth.accounts.recover() function. The data will be UTF-8 HEX decoded and enveloped as follows: "\x19Ethereum Signed Message:\n" + message.length + message and hashed using keccak256.