Thank you very much for the replies and advices!
The "Just Do It......" example showed me well on how to make objects appear and disappear.
However, although I may sound very clamorous, as I implemented the code,
I felt that the disappearing motion, after the appearing motion, came a little too instantaneous.
I prefer there being some time lag between the appearing and the disappearing of the svg.
And to be much more demanding, I figured that I may want the svg to scale larger as it is gradually disappearing.
I am sorry it may be a turn down of the options @mikel provided me,
but is it possible to create a time lag between appearing and disappearing of a single svg, and also add certain things particularly on either of the motion?
Sincerely,