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Understanding Sort Function in JavaScript.

Understanding Sort Function in JavaScript.

Vishwajeet Raj
·Feb 11, 2022·

2 min read

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Table of contents

  • Sort Function
  • It Gets Tricky.
  • Compare Function
  • Complete Sort Function for Numbers

Sort Function

  • Used to Sort Arrays in JavaScript.
  • This method mutates the original array.
  • By default, the order is ascending but we can change the order.
  • We can also provide our compare function to implement custom sorting.

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As you can the result is fine. This is what we needed Array elements got sorted in ascending order and also the array got mutated.

It Gets Tricky.

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What just happened? Why did element 1 get sorted to its correct position but element 2 didn't get sorted.

Why did the sort function not work as expected (Ascending Order)?

For the above code, the expected result is [1,1,2,8,11,22,45], but we get [1,1,11,2,22,45,8].

Reason

The reason is the sort method converts the elements into strings then compares their sequences of UTF-16 code units values.

Explanation

So the 1 is converted to “1”. When we compare two strings like “1” and “22”, the char code is compared means char code of 1 is 49, whereas char code of 2 is 50. Because of 49 < 50, we get = 1, 1, 11 before 2, 22.

This is where compare Function comes to the rescue.

Compare Function

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The compare function takes two arguments. The two arguments are taken as from array on index [0,1] , [1,2] … [arrayLength-2, arrayLength-1] for comparing the pair of elements.

The sorting of elements is based on the return value of compareFunction for each pair of comparisons.

If the function returns a value

  • 0 then the position of a and b is swapped.

  • <=0 then there is no change in position

The function can also be written as

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Complete Sort Function for Numbers

Ascending Order

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Descending Order

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Sort Function for String

There is no need for the compareFunction for sorting strings. We can use the default sort method to sort strings.

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