Event Types
An event is simply a notification or a "triggered
" alert within the JavaScript runtime. These notifications can represent practically anything but are a means to invoke one or more of your own functions when such an event occurs.
When a web page loads, the browser will typically display content as soon as it is available. This means some content will be presented to the user before the entire page has finished downloading. The browser does this to prevent long-loading assets from withholding other content from being available to the user.
Now, imagine you want to invoke a function immediately within a web page to rotate an image. JavaScript code embedded into a web page is able to run immediately once it has been parsed by the JavaScript engine, which could possibly be before the image in question is available. To overcome this conundrum, JavaScript provides an onload
event, which is dispatched as soon as all the page's content has finished downloading...