Mastering Blockchain - Second Edition

Events

Events in Solidity can be used to log certain events in EVM logs. These are quite useful when external interfaces are required to be notified of any change or event in the contract. These logs are stored on the blockchain in transaction logs. Logs cannot be accessed from the contracts but are used as a mechanism to notify change of state or the occurrence of an event (meeting a condition) in the contract.

In a simple example here, the valueEvent event will return true if the x parameter passed to function Matcher is equal to or greater than 10:

pragma solidity ^0.4.0; contract valueChecker { uint8 price=10; event valueEvent(bool returnValue); function Matcher(uint8 x) public returns (bool) { if (x>=price) { valueEvent(true); return ...