Move objects at the beginning of array using sort()

Question

I need to sort an object array by date values:

array.sort(function(a,b){
return new Date(b.date) - new Date(a.date);
})

But if date is undefined, it should be placed at the beginning. With my code shown above, the empty datasets will be placed at the end.

sounds like the quick and dirty would be to just reverse the array?... array.sort(/* ...other code here... */).reverse() — Matt Oestreich
– Matt Oestreich, Commented Dec 29, 2019 at 1:21
@MattOestreich No, as the sorting of all other elements should not be reversed — user3142695
– user3142695, Commented Dec 29, 2019 at 1:21
What are the possible values for the date field? Is it expected to be string or integer? — Hugo G
– Hugo G, Commented Dec 29, 2019 at 1:24
@MisterJojo that's why I asked about the input. The Date constructor also supports strings — Hugo G
– Hugo G, Commented Dec 29, 2019 at 1:29

score 4 · Accepted Answer · 2019-12-29 03:42:08Z

4

const array = [
  { date: 624000, name: 'Eddison', },
  { date: 224000, name: 'Bobby', },
  {               name: '--no date 2' },
  { date: 924000, name: 'Fred', },
  { date: 124000, name: 'Abe', },
  {               name: '--no date 1' },
  { date: 424000, name: 'David', },
  { date: 324000, name: 'Catheryn', },
];

// assuming there is no 0 date
array.sort(function(a, b) {
  return (a.date && b.date)
      ? new Date(b.date) - new Date(a.date)
      : (a.date || 1) - (b.date || 1); 
});

//result
array.forEach(elem => console.log(JSON.stringify(elem)));

note if you care about the difference between a date of 0 and a undefined date then

  return (a.date !== undefined && b.date !== undefined)

edited Dec 29, 2019 at 3:42

answered Dec 29, 2019 at 1:23

user128511

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12 Comments

Mister Jojo Over a year ago

your a and b are numbers, no need to convert them to dates to make a sort...

user128511 Over a year ago

Of course but the OP didn't show what their dates were and numbers work just fine as place holders for whatever they had.

Hugo G Over a year ago

Note that the OP clarified they have ISO date strings

Matt Oestreich Over a year ago

@HubertGrzeskowiak yep you are correct, I just tested in Chrome and it works.. This does not appear to work in Firefox.. whew, I was going crazy for a second there lol. Thank you so much for helping me grasp this!

Mister Jojo Over a year ago

this code is OK on Chrome, but wrong on FireFox

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