gistfile1.js

function checkWord( board, word ) {
  const graph = board.map((row, rowNumber) => {
    return row.map((letter, position) => {
      return {
        name: letter,
        neighbours: getNeighbours(rowNumber, position, board),
        index: rowNumber * board.length + position
      };
    });
  });
  let res = false;
  for (let i = 0; i < graph.length; i++) {
    for (let j = 0; j < graph[i].length; j++) {
      if (graph[i][j].name === word[0]) {
        if (word[1] === undefined) {
          res = true;
          break;
        }
        res = searchNext(word, 1, graph[i][j], graph, [graph[i][j]['index']]);
        if (res) {
          break;
        }
      }
    }
  }
  return res;
}

function searchNext(word, index, point, graph, been) {
  let status = false;
  const candidates = checkNeighbours(point, word[index], graph, been);
  candidates.forEach(candidate => {
    if (status) {
      return;
    }
    if (index === word.length - 1) {
      if (candidate.name === word[index]) {
        status = true;
      }
    } else {
      const beenCopy = been.map(el => el);
      beenCopy.push(candidate.index);
      if (searchNext(word, index +1, candidate, graph, beenCopy)) {
        status = true;
      }
    }
  });
  return status;
}

function checkNeighbours(point, letter, graph, been) {
  let row;
  let index;
  return point.neighbours
  .filter(globalIndex => {
    row = Math.floor(globalIndex/graph.length);
    index = globalIndex % graph.length;
    if ((letter === graph[row][index]['name']) && (!been.includes(globalIndex))) {
      return true;
    }
  })
  .map(globalIndex => {
    row = Math.floor(globalIndex/graph.length);
    index = globalIndex % graph.length;
    return graph[row][index];
  });
}

function getNeighbours(row, index, board) {
  const neighbours = [];
  for (let i = row-1; i <= row+1; i++) {
    if (board[i] === undefined) {
      continue;
    }
    for (let j = index-1; j <= index+1; j++) {
      if ((i === row) && (j === index)) j++;
      if (board[i][j] !== undefined) {
        neighbours.push(i*board.length+j);
      }
    }
  }
  return neighbours;
}