A quick Connect Four app build with a single class. Has a stupid AI, simulate, and user interaction. In ramda REPL: https://goo.gl/WBd2jL

connect-four.js

const { log, clear } = console

const reduceI = addIndex(reduce);

const HUMAN = 'X';
const COMPUTER = 'O';

class Board {
  constructor({
    rows = 4,
    columns = 4,
    player1 = HUMAN,
    player2 = COMPUTER,
  } = {}) {
    this.rows = rows;
    this.columns = columns;
    this.player1 = player1;
    this.player2 = player2;

    // Row :: Array<string|nil>
    // Board :: Array<Rows>
    this.board = [];
    for (let i = 0; i < this.rows; i++) {
      let _column = [];
      for (let j = 0; j < this.columns; j++) {
        _column.push(null);
      }
      this.board.push(_column)
    };
  }
  
  print() {
    for (let i = this.rows - 1; i >= 0; i--) {  
      compose(
        log,
        join('|'),
        map(when(isNil, always('-'))),
      )(this.board[i]);
    }
    compose(log, join(' '), times(add(1)))(this.columns);
    return this;
  }
  
  _traverse = (cb) => ({ player, column }) => {
    for (let i = 0; i < this.rows; i++) {
      for (let j = 0; j < this.columns; j++) {
        const currColumn = j + 1;
        if (currColumn !== column) continue;

        const currValue = this.board[i][j];
        if (isNil(currValue)) {
          return cb({ 
            r: i, 
            c: j,
            player,
            column,
          });
        }
      }
    }
    return cb(null);
  }

  move = this._traverse(({ r, c, player, column }) => {
    this.board[r][c] = player;
  });

  moveIsValid = this._traverse(ifElse(isNil, F, T));
  
  isFull() {
    for (let i = 0; i < this.rows; i++) {
      for (let j = 0; j < this.columns; j++) {
        const currValue = this.board[i][j];
        if (isNil(currValue)) {
          return false;
        }
      }
    }
    return true;
  }

  movePlayer = player => {
    for (let i = 0; i < this.rows; i++) {
      for (let j = 0; j < this.columns; j++) {
        const currValue = this.board[i][j];
        if (isNil(currValue)) {
          this.board[i][j] = player;
          return this;
        }
      }
    }
    throw new Error('No Moves Available');
  }

  movePlayer1 = () => this.movePlayer(this.player1);
  movePlayer2 = () => this.movePlayer(this.player2);

  movePlayer1ThenAI = ({ column }) => {
    log('-----------Making move-----');
    this.move({ player: this.player1, column });
    this.print();
    this.movePlayer2();
    this.print();
  }

  simulate() {
    try {
      while(!this.isFull()) {
        this.movePlayer1();
        this.print();
        this.movePlayer2();
        this.print();
      }
    } catch(e) {
      log(e);
    }
  }
}

const game = new Board({ rows: 7, columns: 7 });

window.onkeyup = (e) => {
  const column = parseInt(e.key, 10);
  if (column > game.columns) {
    log('cannot make move');
  } else {
    game.movePlayer1ThenAI({ column });  
  }
}

// clear();
// TYPE BELOW:
// 1231

const foo = 'end';
foo