Argument passed to the callback when a request finishes successfully or erroneously.
NOTE This is an abstract type. Any object meeting this description can be used where this type is used.
Error code. Returns 0 if success is true.
Error code will be 0 if success is true, nonzero otherwise. If the error
was generated by the operating system, that system's error value is used.
Otherwise, this value will be -1.
Error message, if any returned.
Error message, if any returned.
Will be undefined if success is true.
Indicates if the operation succeeded.
Indicates if the operation succeeded.
Returns true if request succeeded, false otherwise.