How to implement Insertion sort algorithm in JavaScript

In this tutorial, we will learn about the insertion sort algorithm and its implementation in JavaScript.

Insertion sort maintains a sorted list and unsorted list in the same array. it finds the correct position to insert the item in the sorted list that’s why it’s called insertion sort.

In the below diagram, red color items are sorted and yellow ones are unsorted.

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Let’s write an algorithm.

function insertionSort(array,length=array.length){
  return array
}

Next, we need to create a for loop which starts from 1. Inside the for loop we declared and initialized the temp variable with arr[i].

function insertionSort(array,length=array.length){
  for(var i = 1 ;  i < length ; i++){
    var temp = arr[ i ];
  }
  return array;
}

In nested for loop we are moving backward.Inside the nested for loop we need to swap the arr[j+1] = arr[j].

function insertionSort(array,length=array.length){
  for(var i = 1 ;  i < length ;i++){
    var temp = array[ i ];
    for(var j = i-1 ; j>-1 && array[ j ]>temp; j--){
       array[ j+1 ] = array[ j ];
    }
  }
  return array;
}

final step update the array[i+1] with temp value;

Completed algorithm

function insertionSort(array,length=array.length){
  for(var i = 1 ;  i < length ;i++){
    var temp = array[ i ];
    for(var j = i-1 ; j>-1 && array[ j ]>temp; j--){
       array[ j+1 ] = array[ j ];
    }
    array[ j+1] = temp;
  }
  return array;
}

console.log(insertionSort([4,1,3,7,2])) // [1, 2, 3, 4, 7]

Visualization

Time complexity

• Best case - O(n)
• Average case - O(n²)
• Worst case - O( n ²)

Space complexity - O(n)