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Sort an Array of Integers in JavaScript and Node.js

Sorting data is a common task in programming. JavaScript provides a .sort(comparator) method on arrays allowing you to sort data with custom comparator. A comparator represents a compare function determining which element comes before the other.

When sorting integers, a custom compare function comes handy because you can ensure the sorting order and not rely on the default JavaScript sorting behavior.

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Sort an Array of Integers

Sorting a list of numbers in JavaScript can have two directions. Either sort the values ascending or descending. Using the .sort() method on JavaScript arrays will always try to sort the values in ascending order.

Use a Compare Function When Sorting Integers

Using .sort() on arrays without providing a compare function will convert each item to a string. Then, JavaScript uses the string representation of each item and compares them in UTF-16 code units order.

And here’s the catch. You want the number 9 come before the number 80 when sorting data. But because JavaScript casts both numbers two strings, the sorting order is from Unicode and the 80 comes before 9.

Bummer!

That’s the reason you should sort integer values with a custom comparator.

Sort Ascending (Lowest to Highest)

The following code snippet shows the sorting of a list of integer values. It sorts the values in ascending order. A custom comparator receives two array items. You can ensure the ascending order by subtracting the b from a:

const array = [ 1, 6, 4, 9, 3 ]

// sort ascending (1 to X)
const sorted = array.sort((a, b) => {  
  return a - b
})

// [ 1, 3, 4 6, 9]

Looks good! If you want, you can copy the code snippet and test it out in the developer tools of your browser.

Sort Descending (Highest to Lowest)

You can also sort a list of integers in descending order. When sorting the values from highest to lowest, you can flip the numbers in the calculation of the custom compare function:

const array = [ 1, 6, 4, 9, 3 ]

// sort descending (X to 1)
const sorted = array.sort((a, b) => {  
  return b - a
})

// [ 9, 6, 4, 3, 1]

You may check out the details about Array#sort in the MDN docs.

Sort Will Change Your Array

One thing to remember when using the .sort() method: it modifies your array. After the sort operation, your original array contains the sorted values.

Enjoy sorting!

Mentioned Resources

Marcus Pöhls

Marcus is a fullstack JS developer. He’s passionate about the hapi framework for Node.js and loves to build web apps and APIs. Creator of Futureflix and the “learn hapi” learning path.

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