Question 184518 in Javascript Question posted in
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Javascript – js sort not consistent on multi sort

I get two different resulting sort orders after sorting my array twice using the native sort method in javascript. I’m sorting by the field ‘date’ and ‘createdAt’. I would expect to get the same order of descending results each time I pass the same array to the algorithm but I get a different resulting order each time. Why is that? Example below.

const arr = [
    {"id": 0, 
     "date": new Date("2023-06-02T00:00:00.000Z"), 
     "createdAt": new Date("2023-06-05T01:48:37.586Z")
    },
    {
        "id": 1,
        "date": new Date("2023-06-03T00:00:00.000Z"),
        "createdAt": new Date("2023-06-04T01:31:35.901Z"),
    },
    {
        "id": 2,
        "date": new Date("2023-06-03T00:00:00.000Z"),
        "createdAt": new Date("2023-06-04T17:19:14.733Z"),
    },
    {
        "id": 3,
        "date": new Date("2023-06-03T00:00:00.000Z"),
        "createdAt": new Date("2023-06-04T21:10:26.454Z"),
    },
    {
        "id": 4,
        "date": new Date("2023-06-03T00:00:00.000Z"),
        "createdAt": new Date("2023-06-04T21:11:53.192Z"),
    },
    {
        "id": 5,
        "date": new Date("2023-06-03T00:00:00.000Z"),
        "createdAt": new Date("2023-06-04T21:13:13.879Z"),
    },
    {
        "id": 6,
        "date": new Date("2023-06-03T00:00:00.000Z"),
        "createdAt": new Date("2023-06-04T21:15:46.841Z"),
    },
    {
        "id": 7,
        "date": new Date("2023-06-03T00:00:00.000Z"),
        "createdAt": new Date("2023-06-04T21:16:45.006Z"),
    },
    {
        "id": 8,
        "date": new Date("2023-06-04T00:00:00.000Z"),
        "createdAt": new Date("2023-06-04T17:21:19.906Z"),
    },
    {
        "id": 9,
        "date": new Date("2023-06-04T00:00:00.000Z"),
        "createdAt": new Date("2023-06-04T21:01:39.286Z"),
    },
    {
        "id": 10,
        "date": new Date("2023-06-04T00:00:00.000Z"),
        "createdAt": new Date("2023-06-04T21:09:48.776Z"),
    },
    {
        "id": 11,
        "date": new Date("2023-06-04T00:00:00.000Z"),
        "createdAt": new Date("2023-06-04T21:27:45.701Z"),
    }
]

function sortItems(items) {
  return items.toSorted((a, b) => {
    // do comparison
    if (a.date > b.date) {
      return -1
    } else if (a < b.date) {
      return 1
    } else {
      if (a.createdAt > b.createdAt) {
        return -1
      } else if (b.createdAt < b.createdAt) {
        return 1
      } else {
        return 0
      }
    }
  })
}

const sort_1 = sortItems(arr)
console.log(sort_1)
const sort_2 = sortItems(sort_1)
console.log(sort_2)

The result is two diffent resulting sort orders. Why is that?

Tags:

2

Answers


  1. 0 
    const arr = [{
    "id": 0,
    "date": new Date("2023-06-02T00:00:00.000Z"),
    "createdAt": new Date("2023-06-05T01:48:37.586Z")
  },
  {
    "id": 1,
    "date": new Date("2023-06-03T00:00:00.000Z"),
    "createdAt": new Date("2023-06-04T01:31:35.901Z"),
  },
  {
    "id": 2,
    "date": new Date("2023-06-03T00:00:00.000Z"),
    "createdAt": new Date("2023-06-04T17:19:14.733Z"),
  },
  {
    "id": 3,
    "date": new Date("2023-06-03T00:00:00.000Z"),
    "createdAt": new Date("2023-06-04T21:10:26.454Z"),
  },
  {
    "id": 4,
    "date": new Date("2023-06-03T00:00:00.000Z"),
    "createdAt": new Date("2023-06-04T21:11:53.192Z"),
  },
  {
    "id": 5,
    "date": new Date("2023-06-03T00:00:00.000Z"),
    "createdAt": new Date("2023-06-04T21:13:13.879Z"),
  },
  {
    "id": 6,
    "date": new Date("2023-06-03T00:00:00.000Z"),
    "createdAt": new Date("2023-06-04T21:15:46.841Z"),
  },
  {
    "id": 7,
    "date": new Date("2023-06-03T00:00:00.000Z"),
    "createdAt": new Date("2023-06-04T21:16:45.006Z"),
  },
  {
    "id": 8,
    "date": new Date("2023-06-04T00:00:00.000Z"),
    "createdAt": new Date("2023-06-04T17:21:19.906Z"),
  },
  {
    "id": 9,
    "date": new Date("2023-06-04T00:00:00.000Z"),
    "createdAt": new Date("2023-06-04T21:01:39.286Z"),
  },
  {
    "id": 10,
    "date": new Date("2023-06-04T00:00:00.000Z"),
    "createdAt": new Date("2023-06-04T21:09:48.776Z"),
  },
  {
    "id": 11,
    "date": new Date("2023-06-04T00:00:00.000Z"),
    "createdAt": new Date("2023-06-04T21:27:45.701Z"),
  }
];

let dessort = arr.sort((a, b) => {
  return (a.date - b.date) && (a.createdAt - b.createdAt);
});

console.log(dessort);
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  2. 0

    You could simplify your code considerably. And make it more reliable and easier to read:

    const arr = [{"id": 0,"date": new Date("2023-06-02T00:00:00.000Z"),"createdAt": new Date("2023-06-05T01:48:37.586Z")},
{"id": 1,"date": new Date("2023-06-03T00:00:00.000Z"),"createdAt": new Date("2023-06-04T01:31:35.901Z")},
{"id": 2,"date": new Date("2023-06-03T00:00:00.000Z"),"createdAt": new Date("2023-06-04T17:19:14.733Z")},
{"id": 3,"date": new Date("2023-06-03T00:00:00.000Z"),"createdAt": new Date("2023-06-04T21:10:26.454Z")},
{"id": 4,"date": new Date("2023-06-03T00:00:00.000Z"),"createdAt": new Date("2023-06-04T21:11:53.192Z")},
{"id": 5,"date": new Date("2023-06-03T00:00:00.000Z"),"createdAt": new Date("2023-06-04T21:13:13.879Z")},
{"id": 6,"date": new Date("2023-06-03T00:00:00.000Z"),"createdAt": new Date("2023-06-04T21:15:46.841Z")},
{"id": 7,"date": new Date("2023-06-03T00:00:00.000Z"),"createdAt": new Date("2023-06-04T21:16:45.006Z")},
{"id": 8,"date": new Date("2023-06-04T00:00:00.000Z"),"createdAt": new Date("2023-06-04T17:21:19.906Z")},
{"id": 9,"date": new Date("2023-06-04T00:00:00.000Z"),"createdAt": new Date("2023-06-04T21:01:39.286Z")},
{"id":10,"date": new Date("2023-06-04T00:00:00.000Z"),"createdAt": new Date("2023-06-04T21:09:48.776Z")},
{"id":11,"date": new Date("2023-06-04T00:00:00.000Z"),"createdAt": new Date("2023-06-04T21:27:45.701Z")}];

function byDates(a,b){return b.date-a.date || b.createdAt-a.createdAt;}

const sort_1 = arr.sort(byDates)
console.log(sort_1)
const sort_2 = sort_1.sort(byDates)
console.log(sort_2)

    The expression after the "or" (||) will only come into action if the result of the first part is not equal to 0.

    Please note:
    Assigning the arr.sort(byDates) results to a new variable, or in this case: a new constant, makes very little sense as Array.prototype.sort() works "in place". This means that the source array will be changed and only a reference to that same (but re-ordered) array will be returned.

    If you want to preserve the original sort order in arr you should Array.prototype.slice() the array before .sort()ing it:

    const sort_1 = arr.slice().sort(byDates);
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