# Using merge sort to recursive sort an array JavaScript

We are required to write a JavaScript function that takes in an array of Numbers. The function should sort the array using the merge sort algorithm.

## Merge Sort

Merge Sort is made up of two parts or processes −

• a recursive part that splits up a collection into single units,
• and then an iterative part that combines them back together in the right order.

## Example

const arr = [23, 4, 67, 32, 1, 7, 56, 5, 89];
const mergeSort = arr => {
if (arr.length < 2){
return arr;
}
const middle = Math.floor(arr.length / 2);
const left = arr.slice(0, middle), right = arr.slice(middle, arr.length);
return merge(mergeSort(left), mergeSort(right));
};
const merge = (left, right) => {
const res = [];
while (left.length && right.length) {
if (left[0] <= right[0]){
res.push(left.shift());
}
else{
res.push(right.shift());
};
}
while (left.length){
res.push(left.shift());
};
while (right.length){
res.push(right.shift());
};
return res;
};
console.log(mergeSort(arr));

## Output

And the output in the console will be −

[
1, 4, 5, 7, 23,
32, 56, 67, 89
]