Number of Increasing Paths in a Grid LeetCode solution in JavaScript

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var countPaths = function (grid) {
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  let mod = Math.pow(10, 9) + 7;
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  let result = 0;
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  let rows = grid.length,
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    columns = grid[0].length;
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  let dp = Array(rows)
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    .fill(null)
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    .map((_) => Array(columns).fill(0));
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  const dfs = (r, c, preVal) => {
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    if (r < 0 || r == rows || c < 0 || c == columns || grid[r][c] <= preVal)
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      return 0;
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    if (dp[r][c]) return dp[r][c];
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    return (dp[r][c] =
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      (1 +
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        dfs(r + 1, c, grid[r][c]) +
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        dfs(r - 1, c, grid[r][c]) +
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        dfs(r, c + 1, grid[r][c]) +
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        dfs(r, c - 1, grid[r][c])) %
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      mod);
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  };
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  for (let i = 0; i < rows; i++) {
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    for (let j = 0; j < columns; j++) {
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      result += dfs(i, j, -1) % mod;
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    }
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  }
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  return result % mod;
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};