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.

CodePudding user response：

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

CodePudding user response：

So check if the age is defined. If not set it to a large number to force it to the end.

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

function getAge (obj) {
  return obj.age === undefined ? Number.MAX_VALUE : obj.age;
}

names.sort(function (a, b) {
  // if (a.age === b.age) {
  //   return a.name.localeCompare(b.name);
  // }
  return getAge(a) - getAge(b);
})

console.log(names);

CodePudding user response：

You could check for the property and if not exist, move this objects to bottom. for the rest sort by age.

const
    names = [{ name: "John", age: 27 }, { name: "Charles" }, { name: "Ellen", age: 30 }, { name: "Mario" }, { name: "Emanuelle", age: 18 }];
    
names.sort((a, b) =>
    ('age' in b) - ('age' in a) || // sort object without `age` to bottom
    a.age - b.age                  // sort by `age`
);

console.log(names);

.as-console-wrapper { max-height: 100% !important; top: 0; }

CodePudding user response：

Sort not work properly because any number operation with undefined are NaN I.E: 1 - undefined = NaN.

For this sort, you can use destructuring defaults, try this:

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

names.sort(  ({age : agea = Number.MAX_VALUE}, {age : ageb = Number.MAX_VALUE}) => agea-ageb)

console.log(names)