JavaScript Array Sort
Alphabetic SortArray sort()Array reverse() Array toSorted() Array toReversed() Sorting Objects | Numeric SortNumeric SortRandom Sort Math.min() Math.max() Home made Min() Home made Max() |
See Also:
Sorting an Array
Thesort() method sorts an array alphabetically:
Reversing an Array
Thereverse() method reverses the elements in an array:
By combiningsort() andreverse(),you can sort an array in descending order:
Example
fruits.sort();
fruits.reverse();
JavaScript Array toSorted() Method
ES2023 added thetoSorted() method as a safe wayto sort an array without altering the original array.
The difference betweentoSorted() andsort()is that the first method creates a new array, keeping the original array unchanged, while the last method alters the original array.
Example
const sorted = months.toSorted();
JavaScript Array toReversed() Method
ES2023 added thetoReversed() method as a safe wayto reverse an array without altering the original array.
The difference betweentoReversed() andreverse() is that the first methodcreates a new array, keeping the original array unchanged, while the last method alters the original array.
Example
const reversed = months.toReversed();
Numeric Sort
By default, thesort() function sorts values asstrings.
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, thesort() method will produce incorrect result when sorting numbers.
You can fix this by providing acompare function:
Example
points.sort(function(a, b){return a - b});
Use the same trick to sort an array descending:
Example
points.sort(function(a, b){return b - a});
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 thesort() 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 beforeb.
If the result is positive,b is sorted beforea.
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, thesort() 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:
<button onclick="myFunction2()">Sort Numerically</button>
<p id="demo"></p>
<script>
const points = [40, 100, 1, 5, 25, 10];
document.getElementById("demo").innerHTML = points;
function myFunction1() {
points.sort();
document.getElementById("demo").innerHTML = points;
}
function myFunction2() {
points.sort(function(a, b){return a - b});
document.getElementById("demo").innerHTML = points;
}
</script>
Sorting an Array in Random Order
Using a sort function, like explained above, you can sort an numeric array in random order
Example
points.sort(function(){return 0.5 - Math.random()});
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:
Example
for (let i = points.length -1; i > 0; i--) {
let j = Math.floor(Math.random() * (i+1));
let k = points[i];
points[i] = points[j];
points[j] = k;
}
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 value 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:
Example
points.sort(function(a, b){return a - b});
// now points[0] contains the lowest value
// and points[points.length-1] contains the highest value
Sort Descending:
Example
points.sort(function(a, b){return b - a});
// now points[0] contains the highest value
// and points[points.length-1] contains the lowest value
Note
Sorting a whole array is a very inefficient method if you only want to find the highest (or lowest) value.
Using Math.min() on an Array
You can useMath.min.apply to find the lowest number in an array:
Math.min.apply(null, [1, 2, 3]) is equivalent toMath.min(1, 2, 3).
Using Math.max() on an Array
You can useMath.max.apply to find the highest number in an array:
Math.max.apply(null, [1, 2, 3]) is equivalent toMath.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 ahome made method.
This function loops through an array comparing each value with the lowest value found:
Example (Find Min)
let len = arr.length;
let min = Infinity;
while (len--) {
if (arr[len] < min) {
min = arr[len];
}
}
return min;
}
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 ahome made method.
This function loops through an array comparing each value with the highest value found:
Example (Find Max)
let len = arr.length;
let max = -Infinity;
while (len--) {
if (arr[len] > max) {
max = arr[len];
}
}
return max;
}
Sorting Object Arrays
JavaScript arrays often contain objects:
Example
{type:"Volvo", year:2016},
{type:"Saab", year:2001},
{type:"BMW", year:2010}
];
Even if objects have properties of different data types, thesort() 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:
Example
let x = a.type.toLowerCase();
let y = b.type.toLowerCase();
if (x < y) {return -1;}
if (x > y) {return 1;}
return 0;
});
Stable Array sort()
ES2019revised the Arraysort() 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.
Example
{name:"X00",price:100 },
{name:"X01",price:100 },
{name:"X02",price:100 },
{name:"X03",price:100 },
{name:"X04",price:110 },
{name:"X05",price:110 },
{name:"X06",price:110 },
{name:"X07",price:110 }
];
In the example above, when sorting on price, the result is not allowed to come out with the namesin an other relative position like this:
X03 100
X00 100
X02 100
X05 110
X04 110
X06 110
X07 110
Complete JavaScript Reference
For a complete reference to all JavaScript properties and methods, with full descriptions and many examples, go to:
W3Schools' Full JavaScript Reference.
The reference inludes all JavaScript updates from 1999 to 2025.
