Events
Solidity supports events. Events in Solidity are just like events in other programming languages. Events are fired from contracts such that anybody interested in them can trap/catch them and execute code in response. Events in Solidity are used primarily for informing the calling application about the current state of the contract by means of the logging facility of EVM. They are used to notify applications about changes in contracts and applications can use them to execute their dependent logic. Instead of applications they keep polling the contract for certain state changes; the contract can inform them by means of events.
Events are declared within the contract at the global level and invoked within its functions. An event is declared ...