.focus() event behavior with Javascript

I have these three tabs:

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When a user uses the mouse and clicks on one of the tabs, (Compliance Notes in this example), the proper element on the tabbed page gets focus and is highlighted appropriately.

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However, if the user uses the keyboard and presses the Tab key to highlight the tab they want, and then presses the Enter key to select that tab, the tabbed page gets focus. Then, via JavaScript, I set focus to the proper element on that tabbed page (by using the .focus() method on that element), and the same asp:DropDownList in the example behaves like the user not only selected the element, but clicked on it:

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If you then either hit Enter or Tab, manually, the dropdown list closes and the element looks like it did if the user clicked on the tab versus using the keyboard:

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So, is there a “simple” way, after I use the .focus() method, to then simulate either an Enter or Tab keystroke so the element will have focus but not have the dropdown list triggered? Or is there another way, using the .focus() method or some other approach, to prevent the dropdown list from being triggered when using the keyboard to navigate the page?