Unraveling the nested loop — JavaScript

Have you ever stumbled upon an algorithm problem and realized that a possible solution is a nested loop and wondered — wait where do I start the second iteration from again???

If this is you right now…

Don’t worry — me too!!

Let’s set this iterator straight!! Working with the below example:

let animals = ["duck", "pig", "chicken", "cow"]

To obtain all possible pair combinations of the ‘animals’ array we could use the following:

function unravel(arr){
  for( let i=0; i< arr.length; i++){
    for(let j=0; j< arr.length; j++){
      console.log(arr[i], arr[j])
    }
  }
}
unravel(animals)

In this case the inner loop iterates for every single iteration of the outer for loop and yields sixteen pairs as follows:

input: animals = ["duck", "pig", "chicken", "cow"]
=>          arr[i]     arr[j]         i j
            duck       duck           0 0
            duck       pig            0 1
            duck       chicken        0 2
            duck       cow            0 3
            pig…