Interval List Intersections LeetCode solution in JavaScript

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var intervalIntersection = function (firstList, secondList) {
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  //if a overlap b - a.start >= b.start && a.start <= b.end
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  //if b overlap a - b.start >= a.start && b.start <= a.end
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  //handle empty edge cases
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  if (firstList.length === 0 || secondList.length === 0) {
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    return [];
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  }
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  let merged = [];
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  let i = 0;
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  let j = 0;
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  while (i < firstList.length && j < secondList.length) {
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    let a_overlap_b =
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      firstList[i][0] >= secondList[j][0] &&
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      firstList[i][0] <= secondList[j][1];
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    let b_overlap_a =
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      secondList[j][0] >= firstList[i][0] &&
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      secondList[j][0] <= firstList[i][1];
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    if (a_overlap_b || b_overlap_a) {
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      let start = Math.max(firstList[i][0], secondList[j][0]);
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      let end = Math.min(firstList[i][1], secondList[j][1]);
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      merged.push([start, end]);
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    }
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    if (firstList[i][1] < secondList[j][1]) {
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      i++;
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    } else {
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      j++;
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    }
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  }
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  return merged;
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};