Coloring A Border LeetCode solution in JavaScript

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var colorBorder = function (grid, row, col, color) {
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  const m = grid.length;
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  const n = grid[0].length;
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  const dirs = [-1, 0, 1, 0, -1];
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  const res = [];
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  for (let i = 0; i < m; i++) {
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    res[i] = new Array(n).fill(-1);
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  }
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  const val = grid[row][col];
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  const stack = [];
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  const visited = new Set();
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  visited.add(`${row}#${col}`);
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  stack.push([row, col]);
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  while (stack.length > 0) {
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    const [currRow, currCol] = stack.pop();
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    let isConnected = true;
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    for (let i = 0; i < dirs.length - 1; i++) {
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      const neiRow = currRow + dirs[i];
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      const neiCol = currCol + dirs[i + 1];
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      if (withinBound(neiRow, neiCol)) {
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        if (!visited.has(`${neiRow}#${neiCol}`)) {
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          if (grid[neiRow][neiCol] === val) {
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            visited.add(`${neiRow}#${neiCol}`);
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            stack.push([neiRow, neiCol]);
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          } else {
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            isConnected = false;
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          }
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        }
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      }
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    }
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    if (isBorder(currRow, currCol) || !isConnected)
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      res[currRow][currCol] = color;
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  }
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  for (let i = 0; i < m; i++) {
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    for (let j = 0; j < n; j++) {
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      if (res[i][j] === -1) {
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        res[i][j] = grid[i][j];
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      }
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    }
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  }
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  return res;
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  function withinBound(row, col) {
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    return row >= 0 && col >= 0 && row < m && col < n;
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  }
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  function isBorder(row, col) {
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    return row === 0 || col === 0 || row === m - 1 || col === n - 1;
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  }
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};