SUMMARY

Events are the primary way that JavaScript is tied to web pages. Most common events are defined in the DOM Level 3 Events specification or in HTML5. Even though there is a specification for basic events, many browsers have gone beyond the specification and implemented proprietary events to give developers greater insight into user interactions. Some proprietary events are directly related to specific devices, such as the mobile Safari orientationchange event that is specific to iOS devices.

There are some memory and performance considerations surrounding events. For example:

• It’s best to limit the number of event handlers on a page, since they can take up more memory and make the page feel less responsive to the user.
• Event delegation can be used to limit the number of event handlers by taking advantage of event bubbling.