Sorting an Array
The sort() method sorts an array alphabetically:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>The sort() method sorts an array alphabetically:</p>
<p id="demo1"></p>
<p id="demo2"></p>
<script>
const fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo1").innerHTML = fruits;
fruits.sort();
document.getElementById("demo2").innerHTML = fruits;
</script>
</body>
</html>
Result:
JavaScript Array Sort
The sort() method sorts an array alphabetically:
Banana,Orange,Apple,Mango
Apple,Banana,Mango,Orange
Reversing an Array
The reverse() method reverses the elements in an array.
You can use it to sort an array in descending order:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort Reverse</h2>
<p>The reverse() method reverses the elements in an array.</p>
<p>By combining sort() and reverse() you can sort an array in descending order:</p>
<p id="demo1"></p>
<p id="demo2"></p>
<script>
// Create and display an array:
const fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo1").innerHTML = fruits;
// First sort the array
fruits.sort();
// Then reverse it:
fruits.reverse();
document.getElementById("demo2").innerHTML = fruits;
</script>
</body>
</html>
Result:
JavaScript Array Sort Reverse
The reverse() method reverses the elements in an array.
By combining sort() and reverse() you can sort an array in descending order:
Banana,Orange,Apple,Mango
Orange,Mango,Banana,Apple
Numeric Sort
By default, the sort() function sorts values as strings.
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 incorrect result when sorting numbers.
You can fix this by providing a compare function:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>Sort the array in ascending order:</p>
<p id="demo1"></p>
<p id="demo2"></p>
<script>
const points = [40, 100, 1, 5, 25, 10];
document.getElementById("demo1").innerHTML = points;
points.sort(function(a, b){return a - b});
document.getElementById("demo2").innerHTML = points;
</script>
</body>
</html>
Result:
JavaScript Array Sort
Sort the array in ascending order:
40,100,1,5,25,10
1,5,10,25,40,100
Use the same trick to sort an array descending:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>Sort the array in descending order:</p>
<p id="demo1"></p>
<p id="demo2"></p>
<script>
const points = [40, 100, 1, 5, 25, 10];
document.getElementById("demo1").innerHTML = points;
points.sort(function(a, b){return b - a});
document.getElementById("demo2").innerHTML = points;
</script>
</body>
</html>
Result:
JavaScript Array Sort
Sort the array in descending order:
40,100,1,5,25,10
100,40,25,10,5,1
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:function(a, b){return a – b}
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:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>Click the buttons to sort the array alphabetically or numerically.</p>
<button onclick="myFunction1()">Sort Alphabetically</button>
<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>
</body>
</html>
Result:
Result Shown In Your Browser.
Sorting an Array in Random Order
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>Click the button (again and again) to sort the array in random order.</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
const points = [40, 100, 1, 5, 25, 10];
document.getElementById("demo").innerHTML = points;
function myFunction() {
points.sort(function(){return 0.5 - Math.random()});
document.getElementById("demo").innerHTML = points;
}
</script>
</body>
</html>
Result:
Result Shown In Your Browser.
The Fisher Yates Method
The above example, array.sort(), is not accurate, it will favor some numbers over the 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
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<h3>The Fisher Yates Method</h3>
<p>Click the button (again and again) to sort the array in random order.</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
const points = [40, 100, 1, 5, 25, 10];
document.getElementById("demo").innerHTML = points;
function myFunction() {
for (let i = points.length -1; i > 0; i--) {
let j = Math.floor(Math.random() * i)
let k = points[i]
points[i] = points[j]
points[j] = k
}
document.getElementById("demo").innerHTML = points;
}
</script>
</body>
</html>
Result:
Result Shown In Your Browser.
Find the Highest (or Lowest) Array Value
There are no built-in functions for finding the max or min value in an array.
However, after you have sorted an array, you can use the index to obtain the highest and lowest values.
Sorting ascending:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>The lowest number is <span id="demo"></span>.</p>
<script>
const points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a-b});
document.getElementById("demo").innerHTML = points[0];
</script>
</body>
</html>
Result:
JavaScript Array Sort
The lowest number is 1.
Sorting descending:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>The highest number is <span id="demo"></span>.</p>
<script>
const points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b-a});
document.getElementById("demo").innerHTML = points[0];
</script>
</body>
</html>
Result:
JavaScript Array Sort
The highest number is 100.
Sorting a whole array is a very inefficient method if you only want to find the highest (or lowest) value.
Using Math.max() on an Array
You can use Math.max.apply to find the highest number in an array:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>The highest number is <span id="demo"></span>.</p>
<script>
const points = [40, 100, 1, 5, 25, 10];
document.getElementById("demo").innerHTML = myArrayMax(points);
function myArrayMax(arr) {
return Math.max.apply(null, arr);
}
</script>
</body>
</html>
Result:
JavaScript Array Sort
The highest number is 100.
Math.max.apply(null, [1, 2, 3]) is equivalent to Math.max(1, 2, 3).
Using Math.min() on an Array
You can use Math.min.apply to find the lowest number in an array:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>The lowest number is <span id="demo"></span>.</p>
<script>
const points = [40, 100, 1, 5, 25, 10];
document.getElementById("demo").innerHTML = myArrayMin(points);
function myArrayMin(arr) {
return Math.min.apply(null, arr);
}
</script>
</body>
</html>
Result:
JavaScript Array Sort
The lowest number is 1.
Math.min.apply(null, [1, 2, 3]) is equivalent to Math.min(1, 2, 3).
My Min / Max JavaScript Methods
The fastest solution is to use a “home made” method.
This function loops through an array comparing each value with the highest value found:
Example (Find Max)
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>The highest number is <span id="demo"></span>.</p>
<script>
const points = [40, 100, 1, 5, 25, 10];
document.getElementById("demo").innerHTML = myArrayMax(points);
function myArrayMax(arr) {
let len = arr.length;
let max = -Infinity;
while (len--) {
if (arr[len] > max) {
max = arr[len];
}
}
return max;
}
</script>
</body>
</html>
Result:
JavaScript Array Sort
The highest number is 100.
This function loops through an array comparing each value with the lowest value found:
Example (Find Min)
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>The lowest number is <span id="demo"></span>.</p>
<script>
const points = [40, 100, 1, 5, 25, 10];
document.getElementById("demo").innerHTML = myArrayMin(points);
function myArrayMin(arr) {
let len = arr.length;
let min = Infinity;
while (len--) {
if (arr[len] < min) {
min = arr[len];
}
}
return min;
}
</script>
</body>
</html>
Result:
JavaScript Array Sort
The lowest number is 1.
Sorting Object Arrays
JavaScript arrays often contain objects:
Example
const cars = [
{type:”Volvo”, year:2016},
{type:”Saab”, year:2001},
{type:”BMW”, year:2010}
];
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:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>Sort car objects on age:</p>
<p id="demo"></p>
<script>
const cars = [
{type:"Volvo", year:2016},
{type:"Saab", year:2001},
{type:"BMW", year:2010}
];
displayCars();
cars.sort(function(a, b){return a.year - b.year});
displayCars();
function displayCars() {
document.getElementById("demo").innerHTML =
cars[0].type + " " + cars[0].year + "<br>" +
cars[1].type + " " + cars[1].year + "<br>" +
cars[2].type + " " + cars[2].year;
}
</script>
</body>
</html>
Result:
JavaScript Array Sort
Sort car objects on age:
Saab 2001
BMW 2010
Volvo 2016
Comparing string properties is a little more complex:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Array Sort</h2>
<p>Click the buttons to sort car objects on type.</p>
<button onclick="myFunction()">Sort</button>
<p id="demo"></p>
<script>
const cars = [
{type:"Volvo", year:2016},
{type:"Saab", year:2001},
{type:"BMW", year:2010}
];
displayCars();
function myFunction() {
cars.sort(function(a, b){
let x = a.type.toLowerCase();
let y = b.type.toLowerCase();
if (x < y) {return -1;}
if (x > y) {return 1;}
return 0;
});
displayCars();
}
function displayCars() {
document.getElementById("demo").innerHTML =
cars[0].type + " " + cars[0].year + "<br>" +
cars[1].type + " " + cars[1].year + "<br>" +
cars[2].type + " " + cars[2].year;
}
</script>
</body>
</html>
Result:
Result Shown In Your Browser.