On 07/04/2011 09:01 PM, Dave Raggett wrote:
On 04/07/11 17:57, Olli Pettay wrote:
Mutation listener could easily
implement old/new value handling itself, especially if it knows which
attributes it is interested in.
How exactly would the listener know the previous state?
In the easiest case when the script cares about only one specific attribute:
element.addAttributeChangeListener(
{
prevVal: element.getAttribute("foo"),
handleMutation: function(node, changeTarget) {
if (node == changeTarget) {
// do something with this.prevVal
...
this.prevVal = element.getAttribute("foo");
}
}
});
For a concurrent editing app, it is important to be able to describe
changes reversibly so that you can revert the DOM when a given local
edit isn't accepted, or you need to revert before applying accepted
changes from other clients. I have been able to get this to work fine
with the existing mutation events. Of course, I avoid changing the DOM
within a mutation event listener, but it is easy to defer such changes
by a call to setTimeout, e.g. with a time of zero. I would be quite
happy for the browser to throw an exception when a mutation event
listener tries to call an unsafe API, as this way developers would
rapidly learn of their mistake and switch to better practices.
