Function
Check whether the object variable has been instantiated, that is, whether the value of the instance variable is a valid object.
grammar
IsValid(objectname)
parameter
objectname: The object name to be checked.
Return value
Boolean. If the specified object has created an instance for this case, the IsValid() function returns True, otherwise FALSE is returned. If the value of the parameter obejctname is NULL, the IsValid() function returns NULL.
Example
if (!isValid(options)) return this;