Get the call site in the stack either where at() is called, or where the supplied fn function is called.
at()
fn
If fn is provided, and is not in the current call stack, then undefined will be returned.
undefined
Optional
Get the call site in the stack either where
at()is called, or where the suppliedfnfunction is called.If
fnis provided, and is not in the current call stack, thenundefinedwill be returned.