Modern Full-Stack Development

 A Few Interface for Good Measure
Next up, we find a few interfaces. Note that these are in the TypeScript module that 
state.ts represents, but it’s not in the state object that will ultimately be constructed 
and used in the rest of the app:
interface ISelectedTile { layer: number,
  row: number, column: number, type: number }
interface IScores { player: number, opponent: number }
The first, ISelectedTile, is the definition for an object that describes a tile that is 
currently selected. It contains all the information that is needed to identify a tile (layer, 
row, and column) and it also contains the type of tile it is, and you’ll see why that is 
needed very soon.
The IScores interface describes an object that stores the current score of the player 
and the remote opponent.
Both of these are used to avoid duplication of code: without them, we’d need to 
copy and paste these type definitions in a couple of places in this file’s code – unless we 
wanted to skip typing entirely – neither of which is a great option in general.