How to implement Quicksort algorithm in JavaScript
In this tutorial, we are going to learn about quicksort algorithm and its implementation in JavaScript.
Quicksort
 it is an efficient sorting algorithm for the larger datasets where it
performs faster than the merge sort and heap sort.
 It was Developed by a British computer scientist Tony Hoare in 1959 and published in 1961.
How does quicksort works?
Consider an array which has 5 items [3,6,4,1,2]

First, we need to choose the pivot value from the array, we can choose any thing as a pivot value so that we are choosing last item
2
as a pivot. 
Next, we need to loop through the array and compare with pivot value
2
. If any item which is less than pivot value place that on lefthand side else if any item is greater than the pivot value place that item on the righthand side.
 We need to run the quickSort recursively on right part and left part to get the sorted array.
Quicksort algorithm implementation
Let’s implement the quicksort algorithm in JavaScript.
First, we are creating a quickSort
function with three parameters which are arr
, length
and start
.
arr : unsorted array.
length : How many times we need to loop.
start: loop starting point.
function quickSort(arr,length = arr.length1,start=0){
if(arr.length < 2){
return arr; // base case
}
const pivot = arr[arr.length1];
const left = [ ];
const right = [ ];
}
Next, we are using a while loop which helps us to loop over the items in a unsorted array, if any item is less than pivot value push that item into the left array else push into the right array.
function quickSort(arr,length = arr.length1,start=0){
if(arr.length < 2) {
return arr;
}
const pivot = arr[arr.length1];
const left = [ ];
const right = [ ];
while (start < length) {
if (arr[start] < pivot){
left.push(arr[start])
}
else {
right.push(arr[start])
}
start++ // incrementing start value
}
}
The final step we need to run the quickSort recursively on both lefthand side and righthand side to get the sorted array.
function quickSort(arr, length = arr.length  1, start = 0) {
if (arr.length < 2) return arr // base case
const pivot = arr[arr.length  1]; //pivot value
const left = [ ]; // left handside array
const right = [ ]; // right handside array
while (start < length) { // comparing and pushing
if (arr[start] < pivot){
left.push(arr[start])
}
else {
right.push(arr[start])
}
start++ // incrementing start value
}
// calling quick sort recursively
return [...quickSort(left), pivot, ...quickSort(right)];
}
console.log(quickSort([4, 9, 2, 6, 8, 10, 3, 1, 7, 5]))
//output => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
In the above code we used spread operator to combine the left and right part of the arrays.
Quicksort Time complexity

Average case  O(nlogn)

Best case  O(nlogn)