Events - JavaScript Tutorial - w3Schools - Chapter-15 English

JavaScript Event Handlers
Event handlers can be used to handle and verify user input, user actions, and browser actions:

Things that should be done every time a page loads
Things that should be done when the page is closed
Action that should be performed when a user clicks a button
Content that should be verified when a user inputs data
And more ...
Many different methods can be used to let JavaScript work with events:

HTML event attributes can execute JavaScript code directly
HTML event attributes can call JavaScript functions
You can assign your own event handler functions to HTML elements
You can prevent events from being sent or being handled
And more ...