aggregate not working but find works.

// aggregation wonts fetch any data if you pass strings instead of Date type
// ref: https://stackoverflow.com/questions/47694008/aggregate-date-range-mongoose
const now = new Date();
const fourMonthAgo = new Date(now);
fourMonthAgo.setMonth(fourMonthAgo.getMonth() - 4);
console.log("now.toISOString()");
console.log(now.toISOString());
console.log("fourMonthAgo.toISOString()");
console.log(fourMonthAgo.toISOString());
/* wrong way
console.log(
  (
    await PointsModel.aggregate([
      {
        $match: {
          $and: [
            { createdAt: { $lte: now.toISOString() } },
            { createdAt: { $gte: fourMonthAgo.toISOString() } },
          ],
        },
      },
    ])
  ).length
);
*/
// the right way, the following aggregations work perfectly
    console.log(
      (
        await PointsModel.aggregate([
          {
            $match: {
              $and: [
                {
                  createdAt: {
                    $lte: new Date(now.toISOString()),
                    $gte: new Date(fourMonthAgo.toISOString()),
                  },
                },
              ],
            },
          },
        ])
      ).length
    );
    console.log(
      (
        await PointsModel.aggregate([
          {
            $match: {
              $and: [
                { createdAt: { $lte: new Date(now.toISOString()) } },
                { createdAt: { $gte: new Date(fourMonthAgo.toISOString()) } },
              ],
            },
          },
        ])
      ).length
    );
console.log(
  (
    await PointsModel.find({
      $and: [
        { createdAt: { $lte: now.toISOString() } },
        { createdAt: { $gte: fourMonthAgo.toISOString() } },
      ],
    })
  ).length
);

/* console output:
now.toISOString()
2021-05-26T09:50:48.805Z
fourMonthAgo.toISOString()
2021-01-26T10:50:48.805Z
0
25751
*/