Javascript USES the push method of arrays for quicksort

There are many ways to sort, and this section describes the use of the push method of arrays for quicksort

function quickSort(arr){
 if(arr.length <= 1) return arr;//Determines if the array is valid
 var cut = Math.floor(arr.length/2);//Take the middle subscript
 var left = [],right = [];
 var num = arr.splice(cut,1)[0];//Take basic value
 for(var i = 0;i < arr.length;i ++){
  if(arr[i] < num){
   left.push(arr[i]);//The smaller one is on the left
  }else {
   right.push(arr[i]);//Put the big one on the right
  }
 }
 return quickSort(left).concat(num,quickSort(right));// recursive 
}