How arr.sort() in nodeJS works?

Question

i am getting a strange result using arr.sort() below is the code

const arr=[1,99,102,121,2,2,3,7]
arr.sort()
console.log(arr)

I am getting the following output

[
  1, 1000, 121,  2,
  2,    3,   7, 99
]

can someone please explain what is happening and why?

Also relevant: [How does Javascript's sort() work?](https://stackoverflow.com/q/1494713) | [Why doesn't the sort function of javascript work well?](https://stackoverflow.com/q/6093874) | [Array.sort() doesn't sort numbers correctly](https://stackoverflow.com/q/7000851) | [How to sort an array of integers correctly](https://stackoverflow.com/q/1063007) | [Why does numberArray.sort() not sort numbers correctly in JavaScript?](https://stackoverflow.com/q/11218670) | [Why do javascript sort a numeric array not in numeric order?](https://stackoverflow.com/q/19740047) — VLAZ, May 08 '21 at 12:46
Have you read the [documentation of `Array.sort()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort)? It explains in the first paragraph that it sorts the values as strings. — axiac, May 08 '21 at 14:59

score 1 · Answer 1 · answered May 08 '21 at 12:39

Array.sort accepts a function as parameter:

compareFunction Optional
Specifies a function that defines the sort order. If omitted, the array elements are converted to strings, then sorted according to each character's Unicode code point value.

You need arr.sort((a,b) => a - b)

score 1 · Accepted Answer · edited May 08 '21 at 13:30

As stated in the docs

The default sort order is ascending, built upon converting the elements into strings, then comparing their sequences of UTF-16 code units values.

Thus your values are converted to strings first and then compared lexicographic. Ie "101" is less than "2"

If you want to do a numerical sort, you have to provide a compare function

const arr=[1,99,102,121,2,2,3,7]
arr.sort((a,b) => a-b);
console.log(arr);

How arr.sort() in nodeJS works?

2 Answers2