Solve a bug in setting the main entity in the hot zone through the fromElement attribute of the event object_javascript technique

After clicking the hyperlink "Set as main entity", the original prompt box will change color and display the content: "Already set as merged main entity".
Problem: When there is another hot zone b under the hyperlink on the prompt box of hot zone a, and click the hyperlink of the prompt box of hot zone a, the mouseover event of hot zone b will be triggered, causing hot zone a The prompt box will disappear.
I have been thinking about this problem for a long time but can’t find a solution. Last week Zhou Jun reminded me that I can detect the source element of the event. It suddenly occurred to me that IE's event object has an attribute fromElement, and I tested it. Sure enough, after clicking the hyperlink in the prompt box of hot zone a, the fromElement in the mouseover event of hot zone b was null, so it was easy to handle. When the hot zone was displayed In the function of the prompt box in the area, determine whether a fromElement is null, and return if it is null. This problem is solved, although this fromElement only exists in IE's event.