How to pass the method of JavaScript and pass the method with parentheses difference

The function must be bracketed if it is to invoke it for execution. At this point, the function () is actually equal to the function's return value. Of course, some have no return value, but have performed the behavior in the body of the function, this is the fundamental, that is, as long as the parentheses, will execute the function body code.
Without parentheses, the function name is used as a pointer to the function, which is not the result of the function, because the function body code will not be run. It simply passes the address where the body of the function is located and, when needed, finds the function body to perform

How to pass the method of JavaScript and pass the method with parentheses difference