// IF you use in a button
Exit
// if you use in function
function closeWin() {
  myWindow.close();   // Closes the new window
}
// But it will only work when you open a window through your code like this
function openWin() {
  myWindow = window.open("", "myWindow", "width=200, height=100");   // Opens a new window
}
// You can't close the current window that was open by browser. beacuse browser don't give permission for this