Workshop › Chess › Step 43 of 48

Pick the best move

What we are doing

computerMove does what search does at the top level, but remembers which move gave the best score. DEPTH = 3: its move, your answer, its answer. A random fraction below 1 breaks ties, so the computer does not always play the same game.

```js
const DEPTH = 3 // how many moves ahead the computer looks

function computerMove() {
  let best = null
  let bestScore = -Infinity
  for (const m of legalMoves()) {
    const undo = makeMove(m)
    const score = -search(DEPTH - 1) + Math.random() // a tiny random tie-break
    undoMove(undo)
    if (score > bestScore) {
      best = m
      bestScore = score
    }
  }
  return best
}
```

What it means

The loop is search's loop, but it keeps the move with the best score in best.
DEPTH - 1: one move is played here, the rest is looked at by search.
Math.random() is below 1, too small to change which move is really better (a pawn is 100).

Your turn

Under VALUES write DEPTH.
Above const same = ... write computerMove, with an empty line after it.

Skills: Functions

← Thinking ahead Alpha-beta: skip what cannot matter →

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