In computer programming, an event handler is part of event driven programming where the events are created by the framework based on interpreting inputs. Each event allows you to add code to an application-level event generated by the underlying framework, typically GUI triggers such as a key press, mouse movement, action selection, and an expired timer. In addition, events can represent data changes, new data, etc. Specifically, an event handler is an asynchronous callback subroutine that handles inputs received in a program.
A custom event is a programmer created event. For example, you can contrast an event handler with a member event, an OOP concept where you add an event to a class.
Many development environments and compilers provide for event driven programming, a standard set of application events such as startup, end, on click of a button, etc. This section documents the applicaton event handler or an overview for each language.
For OOP languages, do not confuse this section with class member events discussed in the OOP Details section of our Cross Reference Coding Encyclopedia.