At our meetup Saturday, Kiley Dowling pair programmed with me and it was…​ different. But I’ve heard having someone peek over your shoulder whilst solving an algorithm is both helpful and a real world example of coding in the wild. The particular challenge of the day was to create function comparing two arrays with different values, and returning a new array containing unique; one with values unique to each array

My working solution was close, but not quite returning the right answer. Here is the function:

The solution I created before meeting today used the filter() and indexOf() functions. While on some level filtering the function, the results were not quite what I was hoping for:

This was returning an array minus duplicates. Why? Because by concating the two arrays first, there is no comparison done. I knew it was likely an important step to concat the arrays for better comparison, but my naivity on how indexOf() actually works would explain my error. indexOf() is a method of the Array object that returns the index of the first occurence of the specified value, or -1 if not found. The Array being traversed is not augmented, rather a new array is created with elements that returns a true value. The callback function takes three arguments:

1. The value of the index
2. The index argument
3. The Array object.

So a better solution would be to filter the arrays seperately and concat their return values: