Guess the reason why JS cannot capture the mouse up event on the scroll bar_javascript skills

For example, in a web chat room, the scroll bar will automatically scroll down as the content increases.
When the user presses the mouse on the scroll bar, we can assume that he (she) is browsing the chat content, so a good user experience at this time will not allow the scroll bar to scroll automatically.
In order to implement this function, the first thing you may think of is the mouse down and mouse up events.
However, during the specific implementation, we will find that when the left mouse button is pressed and released on the scroll bar, the mouse up cannot be captured. For example,