JavaScript Sorting Arrays

Sorting an Array

The sort() method sorts an array alphabetically:

Reversing an Array

The reverse() method reverses the elements in an array:

By combining sort() and reverse(), you can sort an array in descending order:

JavaScript Array toSorted() Method

ES2023 added the toSorted() method as a safe way to sort an array without altering the original array.

The difference between toSorted() and sort() is that the first method creates a new array, keeping the original array unchanged, while the last method alters the original array.

JavaScript Array toReversed() Method

ES2023 added the toReversed() method as a safe way to reverse an array without altering the original array.

The difference between toReversed() and reverse() is that the first method creates a new array, keeping the original array unchanged, while the last method alters the original array.

Numeric Sort

By default, the sort() function sorts values as strings.

This works well for strings ("Apple" comes before "Banana").

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 incorrect result when sorting numbers.

You can fix this by providing a compare function:

Use the same trick to sort an array descending:

The Compare Function

The purpose of the compare function is to define an alternative sort order.

The compare function should return a negative, zero, or positive value, depending on the arguments:

When the sort() function compares two values, it sends the values to the compare function, and sorts the values according to the returned (negative, zero, positive) value.

If the result is negative, a is sorted before b.

If the result is positive, b is sorted before a.

If the result is 0, no changes are done with the sort order of the two values.

Example:

The compare function compares all the values in the array, two values at a time (a, b).

When comparing 40 and 100, the sort() method calls the compare function(40, 100).

The function calculates 40 - 100 (a - b), and since the result is negative (-60),  the sort function will sort 40 as a value lower than 100.

You can use this code snippet to experiment with numerically and alphabetically sorting:

Sorting an Array in Random Order

Using a sort function, like explained above, you can sort an numeric array in random order

The Fisher Yates Method

The points.sort() method in the example above is not accurate. It will favor some numbers over others.

The most popular correct method, is called the Fisher Yates shuffle, and was introduced in data science as early as 1938!

In JavaScript the method can be translated to this:

Find the Lowest (or Highest) Array Value

There are no built-in functions for finding the max or min value in an array.

To find the lowest or highest valu you have 3 options:

• Sort the array and read the first or last element
• Use Math.min() or Math.max()
• Write a home made function

Find Min or Max with sort()

After you have sorted an array, you can use the index to obtain the highest and lowest values.

Sort Ascending:

Sort Descending:

Using Math.min() on an Array

You can use Math.min.apply to find the lowest number in an array:

Math.min.apply(null, [1, 2, 3]) is equivalent to Math.min(1, 2, 3).

Using Math.max() on an Array

You can use Math.max.apply to find the highest number in an array:

Math.max.apply(null, [1, 2, 3]) is equivalent to Math.max(1, 2, 3).

JavaScript Array Minimum Method

There is no built-in function for finding the lowest value in a JavaScript array.

The fastest code to find the lowest number is to use a home made method.

This function loops through an array comparing each value with the lowest value found:

JavaScript Array Maximum Method

There is no built-in function for finding the highest value in a JavaScript array.

The fastest code to find the highest number is to use a home made method.

This function loops through an array comparing each value with the highest value found:

Sorting Object Arrays

JavaScript arrays often contain objects:

Even if objects have properties of different data types, the sort() method can be used to sort the array.

The solution is to write a compare function to compare the property values:

Comparing string properties is a little more complex:

Stable Array sort()

ES2019 revised the Array sort() method.

Before 2019, the specification allowed unstable sorting algorithms such as QuickSort.

After ES2019, browsers must use a stable sorting algorithm:

When sorting elements on a value, the elements must keep their relative position to other elements with the same value.

In the example above, when sorting on price, the result is not allowed to come out with the names in an other relative position like this:

const fruits = ["Banana", "Orange", "Apple", "Kiwi"];
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