function readDb(cb) {
              fs.exists(t.getDbFilename(), function(exists) {
                if (exists) {
                  fs.readFile(t.getDbFilename(), {encoding: "utf-8"}, cb); 
                } else {
                  cb(null, null); 
                }
              });
            }
function readDb(cb) {
              fs.exists(t.getDbFilename(), function(exists) {
                if (exists) {
                  fs.readFile(t.getDbFilename(), {encoding: "utf-8"}, cb); 
                } else {
                  cb(null, null); 
                }
              });
            }
function readDb ( cb ) { fs . exists ( t . getDbFilename ( ) , function ( exists ) { if ( exists ) { fs . readFile ( t . getDbFilename ( ) , { encoding : "utf-8" } , cb ) ; } else { cb ( null , null ) ; } } ) ; }
Reads the db.json, if it exists

@param cb
Reads the db . json if it exists