How JavaScript simulates the effect of selecting an OPTION element in a Drop-down box

Because we manually interact with an action, the first thing is to change some of its properties, followed by letting it trigger an event. It is easy to understand this. Let the property change, of course, change its intrinsic properties, so setattribute (AAA,BBB) is out, so it is used to set custom attributes (IE678, that's weird). Want to trigger events, we can use FireEvent or Dispathevent, Ali from the Yui Yahoo made a event-simulate, think more comprehensive, we want to go into the depth can refer to.

Here's what I've achieved:

<! DOCTYPE html>  
Of course, this is not rigorous enough, because I am using the human brain to assume some amount of calculation. We need to know if it has changed. So there's a function that compares the values before and after, and this can look here.
 
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