Identifier to avoid in my program



I just write a simple program to make a ball bouncing with a start button. When I click this button I call a start function in my program. My program doesn’t work. I find the trouble. I use a function named “start” and I think this function is already used in or elsewhere in Javascript.
My questions is

  1. “how can I know about a function name already defined”
  2. “is there a list of function name to avoid ?”
  3. "is there a way to use function name in my program used elsewhere ?

Thanks for ypour anwers

Christophe from France