How does sort() works in JavaScript?

Question

I am using sort() for quite sometime in JavaScript but today I encountered something which is confusing.

Example 1
Here is a snapshot of my chrome console where I am trying to sort an array.

Step 1. aa is an array decalred with some integer values.
Step 2. Result of aa.sort() is unexpected, as yellow highlights clearly shows that that array is not sorted.
Step 3. Sorting the array using a compare function ** inside the sort. And this works perfectly.

Example 2
Here is another example -
.
Simply using **sort() sorts the array in default ascending order while same is not happening in Example 1.

I want to know exactly what goes inside sort() method.

Possible duplicate of [Array.sort() doesn't sort numbers correctly](https://stackoverflow.com/questions/7000851/array-sort-doesnt-sort-numbers-correctly) — Sebastian Simon, Aug 12 '18 at 06:31
You say it's integers, are you sure it's not rather strings? — Joel, Aug 12 '18 at 07:04

score 5 · Accepted Answer · answered Aug 12 '18 at 06:28

5

See MDN:

The default sort order is according to string Unicode code points.

And when you sort by string, 100 is smaller than 20 because it tests character-by-character.

answered Aug 12 '18 at 06:28

Quentin

914,110
126
1,211
1,335

score 2 · Answer 2 · answered Aug 12 '18 at 06:32

From this post:

By default, the sort() method sorts the values as strings in alphabetical and ascending order.

This works well for strings ("Apple" comes before "Banana"). However, if numbers are sorted as strings, "25" is bigger than "100", because "2" is bigger than "1".

Because of this, the sort() method will produce an incorrect result when sorting numbers.

You can fix this by providing a "compare function".

score 1 · Answer 3 · answered Aug 12 '18 at 07:00

1

Array.prototype.sort() is a higher order function. You can use a compare function as an argument to get right results:

let myArray = [6,7,3,5,4,1,45];
myArray.sort((n1, n2) => n1 - n2);
// result => [1, 3, 4, 5, 6, 7, 45]

answered Aug 12 '18 at 07:00

David Herzlos

47
2

The question always says they can pass a sort function to get the correct results. They are asking why they don't get the results they expect with the default sort function. – Quentin Aug 12 '18 at 07:52

score -2 · Answer 4 · answered Aug 12 '18 at 08:04

-2

Numbers are converted to strings. So it thinks like this:

[a, aa, aaa, b, bb, bbb] // makes sense

[1, 11, 111, 2, 22, 222] // um, only makes sense as strings!

answered Aug 12 '18 at 08:04

bob

7,539
2
46
42

How does sort() works in JavaScript?

4 Answers4

Linked

Related