Detect Cycles in 2D Grid LeetCode solution in JavaScript

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const dirs = [
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  [-1, 0],
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  [1, 0],
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  [0, -1],
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  [0, 1],
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];
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var containsCycle = function (grid) {
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  const n = grid.length,
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    m = grid[0].length;
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  const dfs = function (type, i, j, previ, prevj) {
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    if (i < 0 || j < 0 || i == n || j == m) return false;
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    if (grid[i][j] != type) return grid[i][j] == type.toUpperCase();
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    grid[i][j] = grid[i][j].toUpperCase();
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    for (let dir of dirs) {
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      if (i + dir[0] == previ && j + dir[1] == prevj) continue;
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      if (dfs(type, i + dir[0], j + dir[1], i, j)) return true;
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    }
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    return false;
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  };
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  for (let i = 0; i < n; i++)
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    for (let j = 0; j < m; j++) {
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      if (grid[i][j] == grid[i][j].toUpperCase()) continue;
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      if (dfs(grid[i][j], i, j, -1, -1)) return true;
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    }
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  return false;
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};