Web3.js: Get return value from contract method execution

Question

I have ERC-20 token smart-contract which methods I call using sendSignedTransaction from web3.js. After I know transaction is succesfully mined I need to check contract method execution result. How do I do it if all I have is transaction hash?

Example: method transferFrom(from, to, tokens) returns true or false depending on whether transferring was successful. So if I try to transfer 100 tokens from empty wallet, contract method will return false .

Upd: Okay, as I understood there is no way of determining method outcome using txHash after transaction is mined and confirmed. Then which ways exists to handle this case? How can I make sure that tokens were transferred?

Answer 1

您可以在合同代码内部发出一个事件（实际上在ERC20标准中始终存在一个转移事件），然后在web3js内部，使用以下代码行读取所有事件，直到最新的代码块为止：

Events = Contract.eventName({}, {fromBlock: 0, toBlock: 'latest'});