Here are a few tips that can make your life easier.
My advice:It's always a good idea to use these attributes any way because your page will render faster when the attributes are used.
One of the most frustrating experiences a web developer can have is to make a change and not see the change updated when the page is reloaded on the browser. In many cases the change was made correctly, it just isn't rendered by the browser. The problem is caused bu the way the browser saves and reuses information. All developers should know that hitting the 'reload' button does not always load new information. It usually just loads the information from memory (cache). To defeat the browser's caching system (sometimes) press the 'shift' key when clicking on the browser's 'reload' button. This doesn't always work.
My advice:If you're sure you made a change that's not properly rendered by the browser, restart the browser.
It's important to remember that all unique Image objects are restricted to a single width and a single height. This means that when one image source is replaced by another image source it will have the same dimensions as the original Image object. Sometimes this can have desired effects, but not usually.
My advice:Always know (write down) the dimensions of all images you use.
My advice:Use animated GIFs when you want to attract a viewer's attention to something specific.
My advice:Review and use the information in the cache lesson.
One of the things you'll experience when you start writing scripts is that the scritps can get confusing. As a developer, you're responsible for names for things that are very similar. Even in a simple animation, where one image is replaced by another, you have to name the original image source, the replacement image source, and the name for the image object.
My advice:Make your labels as specific as possible.
Keep your naming conventions consistent.
Strive for easy to read code--keep labels short.