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On such occasions, there is no alternative but to use the dreaded browser sniffing to work out what to do. Not all events bubble; for example, focus and blur events do not. A change event, however, will only be fired by elements whose contents can be changed: Its structure reflects our earlier discussions, but it contains some additional code for this particular technique.
Now, the text displayed on-screen for that link will read Google, which matches the link destination that we changed earlier. The removal is done with the following lines:. However, there are no standards to describe how invalid HTML should be interpreted; each browser maker has established their own rules to fill that gap.
Halting bubbling can be done in two ways, as is the case with much event handling: When we mouse-over a thumbnail image, though, the display of that thumbnail changes to show the actual image javsscript which it’s linked, as shown in Figure 4.
So, we must first check that child nodes exist; second, we confirm that there is one and only one child; third, we check whether that one-and-only first child is an image.
Another step to CSS guru-hood is understanding exactly what each browser does wrong, and how you can work around those failings.
Take the following line:. The method returns an array that contains all matching elements Technically, it returns a node collection, but this works just like an array. Changing the text in a page is slightly more complex than changing an attribute; to alter text, you need to understand the concept of text nodes. This technique is useful if your thumbnails aren’t detailed enough to enable users to tell the difference between superficially similar images.
Therefore, as above, the listener function myScriptEventListener can feel safe in using document. Our code will set up listeners only on browsers that do support those methods.
If we include the brackets, we call the method getElementById. Each browser fixes malformed content in a different way, which can generate such horrors as an element that is its own parent node. This comprehensive list of CSS hacks shows you which browsers will be affected by a given hack, if you need to hide certain CSS directives or deliver certain directives to a particular browser. This would mean that we could not check for an element having a specific class using the following:.
Including the brackets would mean that we were testing the return value of the utopiz call, which we do not want to do. The browser software captures the dessign action and sends the event to the right event target.
As always, you can download this excerpt as a PDF if you prefer. Here are the six items in all their detail. We pass the text for the text node as a parameter:. This is a very important distinction. The text node is also floating around, separate dhtl the document. HTML wrb complies with these rules is said to be “valid. But how do you make your code run in response to those events?
If your code uses getElementById and createElementtest for the existence of both methods. The mouse position issue described here is almost the only such situation. We could do this by setting up an event listener that cancelled the default action of that type of event.