JavaScript simulation select implementation code_form special effects

I have recently been confused about closures and inheritance in JavaScript, so I wrote a small thing to get a feel for it.

JS CSS simulates the Select drop-down box and selects the form effect

It is very common to use the Select syntax to implement the drop-down box in web pages, but have you ever seen it using JS CSS simulated Select drop-down box? And you can select a form. Although the code is a bit complicated, it is very helpful for us to understand this type of special effects.