Dock

Set the Dock's badge

macgap.dock.badge = "10";

Note that the value must be a string, and does not have to be an integer in string form.

macgap.dock.badge = "macgap";

Debugging

If the value is an integer type, Finder will crash and there will be this error on the app's console log:

[Error] Error: -[__NSCFNumber isEqualToString:]: unrecognized selector sent to instance