CSCI 121 - Lecture 16 - JavaScript Event Handling

Topics Covered

• What are JavaScript Events
• HTML (aka JavaScript) events are "things" that happen to HTML elements.
• When JavaScript is used in HTML pages, JavaScript can "react" on these events.
• An HTML event can be something the browser does, or something a user does. Here are some examples of HTML events:
• An HTML web page has finished loading
• An HTML input field was changed
• An HTML button was clicked
• Often, when events happen, you may want to do something.
  
  JavaScript lets you execute code when events are detected.
  
  HTML allows event handler attributes, with JavaScript code, to be added to HTML elements.
• Common HTML Events
• The following are common events that are handled with JavaScript code and by calling JavaScript functions:

• Event	Description
  onchange	An HTML element has been changed
  onclick	The user clicks an HTML element
  onmouseover	The user moves the mouse over an HTML element
  onmouseout	The user moves the mouse away from an HTML element
  onkeydown	The user pushes a keyboard key
  onload	The browser has finished loading the page

• What can JavaScript Do?
• 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 ...