TypeError: xxx is not a function

1. Problem description:

       1. When using the button to monitor an event, an error message as shown below appears:

        

        It is this "xxx is not a function" again, this kind of error is still common, after a investigation, it is finally found that methods are written as method , and it can be solved by changing it, of course, there may be other reasons. . . Here I just record it.