Diagonal Traverse II LeetCode solution in JavaScript

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var findDiagonalOrder = function (nums) {
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  let vals = []; // [row, diagonal value, actual value]
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  for (let i = 0; i < nums.length; i++) {
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    for (let j = 0; j < nums[i].length; j++) {
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      vals.push([i, i + j, nums[i][j]]);
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    }
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  }
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  vals.sort((a, b) => {
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    if (a[1] === b[1]) return b[0] - a[0];
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    return a[1] - b[1];
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  });
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  return vals.map((val) => val[2]);
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};