Adding

Using the spread operator

There are no mutations with this code.

function addItem(items, itemToAdd) { 
   return [. . . Items, itemToAdd]; 
} 

Using the unshift method

The unshift method adds new items to the beginning of an array, and returns the new length
This example will mutate the original array.

function addItem(items, itemToAdd) { 
   return Items.unshift(itemToAdd); 
}