gistfile1.ts

// really more a struct/interface
class DataStore {
   store: (object: any, key: string) => string;
   get: (key: string) => any;
}

class JsonDataStore extends DataStore {
   getRawJson: () => string;
   
   static create(fileWriter: FileWriter): JsonDataStore {
      return {
         get: (key: string) => JSON.parse(fileWriter.readAll())[key],
         
         store: function(object: any, key: string): string {
            var allData = JSON.parse(fileWriter.readAll())[key];
            allData[key] = object;
            return fileWriter.writeAll(JSON.stringify(allData));
         },
         
         getRawJson: () => fileWriter.readAll()
      }
   }
}
 
var store = JsonDataStore.create(someRandomFileWriter);
store.store(myRandomObject, 'foo');

interface FileWriter {
	readAll(): string;
	writeAll(s: string): string;
}