FindFour.js

var board = [
  ['-', '-', '-', '-', '-', '-', '-'],
  ['-', '-', '-', '-', '-', '-', '-'],
  ['-', '-', '-', 'R', 'R', 'R', 'R'],
  ['-', '-', '-', 'Y', 'Y', 'R', 'Y'],
  ['-', '-', '-', 'Y', 'R', 'Y', 'Y'],
  ['-', '-', 'Y', 'Y', 'R', 'R', 'R']];

function* getTraverses(matrix) {
  const horizontalSize = matrix[0].length;
  const verticalSize = matrix.length;
  for (let verticalIndex = 0; verticalIndex < verticalSize; verticalIndex++) {
    yield matrix[verticalIndex];
  }

  for (let horizontalIndex = 0; horizontalIndex < horizontalSize; horizontalIndex++) {
    yield matrix.map(subArray => subArray[horizontalIndex]);
  }

  // topRight
  for (let verticalIndex = 0; verticalIndex < (horizontalSize + verticalSize - 1); verticalIndex++) {
    const partial = [];
    let currentVertical = verticalIndex;
    let currentHorizontal = 0;
    while (currentVertical >= 0) {
      if (currentVertical < verticalSize && currentHorizontal < horizontalSize) {
        partial.push(matrix[currentVertical][currentHorizontal]);
      }
      currentVertical--;
      currentHorizontal++;
    }

    yield partial;
  }

  // downRight
  for (let verticalIndex = 0; verticalIndex < (horizontalSize + verticalSize - 1); verticalIndex++) {
    const partial = [];
    let currentVertical = verticalIndex;
    let currentHorizontal = horizontalSize - 1;
    while (currentVertical >= 0) {
      if (currentVertical < verticalSize && currentHorizontal >= 0) {
        partial.push(matrix[currentVertical][currentHorizontal]);
      }
      currentVertical--;
      currentHorizontal--;
    }

    yield partial;
  }
}

const getAccumulator = () => {
  let previousToken;
  let tokenCount;

  return token => {
    if (token === '-') {
      return false;
    }
    if (token === previousToken) {
      tokenCount++;
    } else {
      previousToken = token;
      tokenCount = 1;
    }

    return tokenCount === 4 && previousToken;
  };
};

function connectFour(board) {
  let foundEmpty = false;

  for (const traverse of getTraverses(board)) {
    const accumulator = getAccumulator();
    for (const element of traverse) {
      foundEmpty = foundEmpty || element === '-';
      const result = accumulator(element);
      if (result) {
        return result;
      }
    }
  }

  return foundEmpty
    ? 'in progress'
    : 'draw';
}


console.log(connectFour(board));