Sort() with non-existent values

December 15, 2021

I know that undefined values should be sent to the end of the result, but what about non-existent keys? (Shouldn’t be the same?) It seems sort doesn’t work in those cases:

const names = [
  {
    name: "John",
    age: 27
  },{
    name: "Charles",
  },{
    name: "Ellen",
    age: 30
  },{
    name: "Mario",
  },
  {
    name: "Emanuelle",
    age: 18
  }
]

names.sort(function (a, b) {
  if (a.age > b.age) return 1;

  if (a.age < b.age) return -1;

  return 0;
})

console.log(names) // Sort not working, prints original order

Ideally I want to modify the "names" array and not create/reassign more variables.

>Solution :

Your default sort solution is set to keep the item in its current position –> return 0. You could provide another conditional that captures undefined and return -1

const
names = [{ name: "John", age: 27 }, { name: "Charles" }, { name: "Ellen", age: 30 }, { name: "Mario" }, { name: "Emanuelle", age: 18 }];

names.sort(function (a, b) {
  if(b.age === undefined) return -1;
  if (a.age > b.age) return 1;
  if (a.age < b.age) return -1;
  return 0;
})

console.log(names) // Sort not working, prints original order