Word search solution with unique cell and adjacent cell branching logic

wordSearchImprovement2.js

var exist = function(board, word) {
    var seen = [];
    var targetCharIdx = 0;
    var result = {
        found: false
    };
    for (var i = 0; i < board.length; i++) {
        for (var j = 0; j < board[0].length; j++) {
          if (board[i][j] === word[targetCharIdx]) {
            seen.push([i,j]);
            targetCharIdx++;
            existHelper(board, word, seen, result, targetCharIdx, [i,j])
            targetCharIdx--;
            seen.pop();
          }
        }
    }
    return result.found;
};

var existHelper = function(board, word, seen, result, targetCharIdx, currCell) {
  if (word.length === seen.length) {
    if (wordMatches(word, seen, board)) {
          result.found = true;
    }
  }
    var adjCells = adjacentCells(currCell, board);
    for (var i = 0; i < adjCells.length; i++) {
      var adjCell = adjCells[i];
      if (!alreadySeen(adjCell, seen)) {
         seen.push(adjCell);
         existHelper(board, word, seen, result, targetCharIdx, adjCell)
         seen.pop(adjCell)
      }
    }

};



function adjacentCells(currCell, board) {

 return [[currCell[0] + 1, currCell[1]],
         [currCell[0] - 1, currCell[1]],
         [currCell[0], currCell[1] + 1],
         [currCell[0], currCell[1] - 1]
        ]
      .filter(function(cell) {
          return (cell[0] >= 0 && cell[1] >= 0) &&
                 (cell[0] < board.length && cell[1] < board[0].length)
        });
  
};

function alreadySeen(currCell, seen) {
    var lookup = '';
    var currCell = currCell[0].toString() + currCell[1].toString();
    for (var i = 0; i < seen.length; i++) {
        lookup = seen[i][0].toString() + seen[i][1].toString();

        if (lookup === currCell) {
            return true;
        }

    }
    return false;
  
}
var wordMatches = function(word, seen, board) {
    var constructedWord = '';

    seen.forEach(function(coordinate) {
        constructedWord += board[coordinate[0]][coordinate[1]];

    });

    return constructedWord === word;
};