Maximal Rectangle LeetCode solution in JavaScript

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var maximalRectangle = function (matrix) {
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  const m = matrix.length;
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  const n = matrix[m - 1].length;
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  const prefixSum = new Array(m).fill().map(() => new Array(n).fill(0));
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  for (let i = 0; i < m; i += 1) {
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    for (let j = 0; j < n; j += 1) {
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      prefixSum[i][j] = parseInt(matrix[i][j]);
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      if (i > 0 && prefixSum[i][j] > 0) {
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        prefixSum[i][j] += prefixSum[i - 1][j];
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      }
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    }
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  }
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  const getArea = (currentRow) => {
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    let max = 0;
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    for (let i = 0; i < n; i += 1) {
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      const height = currentRow[i];
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      let leftBoundary = i;
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      while (leftBoundary >= 0 && currentRow[leftBoundary] >= currentRow[i]) {
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        leftBoundary -= 1;
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      }
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      let rightBoundary = i;
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      while (rightBoundary < n && currentRow[rightBoundary] >= currentRow[i]) {
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        rightBoundary += 1;
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      }
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      const width = rightBoundary - leftBoundary - 1;
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      max = Math.max(max, height * width);
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    }
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    return max;
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  };
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  let max = 0;
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  for (let i = 0; i < m; i += 1) {
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    max = Math.max(max, getArea(prefixSum[i]));
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  }
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  return max;
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};