implement enter and leave callbacks, config for add function
implement enter and leave callbacks, config for add function

fateevv/basisjs,basisjs/basisjs,tyanas/basisjs,smelukov/basisjs,fateevv/basisjs,smelukov/basisjs,smelukov/basisjs,tyanas/basisjs,tyanas/basisjs,istrel/basisjs,basisjs/basisjs,istrel/basisjs,basisjs/basisjs,fateevv/basisjs,istrel/basisjs