May 2012
Intermediate to advanced
242 pages
5h 19m
English
Content preview from Maintainable JavaScriptBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Chapter 7. Event Handling
Event handling is an important part of any JavaScript application. All JavaScript is tied to the UI through events, so most web developers spend much of their time coding and modifying event handlers. Unfortunately, this is also an area of JavaScript programming that hasn’t received much attention since the language was first introduced. Even as developers started to embrace more traditional concepts of architecture in JavaScript, event handling was one of those areas in which little has changed. Most event-handling code is very tightly coupled to the event environment (what is available to the developer at the time an event is fired) and therefore is not very maintainable.
Classic Usage
Most developers are familiar with the
event object that is passed into an event
handler when the event is fired. The event
object contains all of the information related to the event, including the event
target as well as additional data based on the event type. Mouse events expose
additional location information on the event
object, keyboard events expose information about keys that have been pressed,
and touch events expose information about the location and duration of touches.
All of this information is provided so that the UI can react
appropriately.
In many cases, however, you end up using a very small subset of the
information present on event. Consider
the following:
// Bad function handleClick(event) { var popup = document.getElementById("popup"); popup.style.left ...Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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