Waits until no elements are matched by the selector. Missing is equivalent to calling .size(0, callback);
.size(0, callback);
//waits until #foo leaves before continuing to the next action. S("#foo").missing()
func_unit.missing(callback) -> FuncUnit
{optional:Function}
a callback that is run after the selector exists, but before the next action
{FuncUnit}
returns the funcUnit for chaining.
Waits until no elements are matched by the selector. Missing is equivalent to calling
.size(0, callback);