Youdao JavaScript monitoring browser problem_javascript skills

But I don’t know if you have encountered such a situation. The newly opened window is opened through instead of window.opener or showModalDialog.
In particular, it is important to note that the address (page) pointed to by this href is not developed by us. For example, we point the href to www.cnblogs.com.
OK, here comes the question: If we have a button on the page where a is located, we can trigger a click event and perform some operations. This click event needs to be triggered after the IE window opened by href is closed. . .
At this time, how do we monitor the window opened by href? (Through javascript, don’t say anything about processes).
Suppose there is a.html as follows:

The current requirement is: click "Link to B. HTML" to open http://www.cnblogs.com.
After the opened new window is closed, the click event of btnParent in a.html is triggered~~~~

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I believe that few people have done such an application or encountered it Such a question. And now I just encountered such a need.
So I post the question here and let everyone help me figure it out.
Although the content of the article is very small, I think such a question is still worthy of being on the homepage. ~~~^_^

The mind is as calm as the mountains and the flowing water is motionless, and the mind is as clear as the fog on Wu Peak.