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2 mins 📖 

Howdy, sorry for the long hiatus. I was busy... planning an underwater holiday park. Nah, I was working hard and getting a little too much imposter syndrome. But now I've taken some helpful advice from myself to cut all that out and acknowledge the brilliant and hardworking developer that I am! And you should do the same. It does wonders for your self-esteem and sanity :)

Anyway, I've been playing with some Codewars katas and getting into the Array.prototype.filter() method in JS, and I like it. It's an almost disturbingly simple way to get some things done.

I was scratching my head about how to complete this task today:

Return an array that contains all values of array a, apart from those that exist in array b.

arrayA = [1, 2, 2, 2, 3]
arrayB = [2]

newArray = [1, 3] // <- make this magic happen!

What filter does for you is filter out any value you wish. You can attach the fitler method to an array, give it a condition, and it will return everything in the array that matches the condition. Note: when I first began using filter, I thought it would remove all values that match the condition, however the values that match the condition are actually kept. This seems a little unintuitive to me, but hey, I didn't write JS ;)

Here is the a solution:

newArray = arrayA.filter(value => !arrayB.includes(value))

In it, we are taking each value of arrayA and if arrayB contains any of these values, we do not display them in our newArray. If the ! was not present, we would create an array containing the values of arrayB that match values in arrayA (i.e. [2, 2, 2]).

Using the filter method takes time to get your head around, but it's worth it! Play around with the example above in your browser console. Also note the Array.prototype.includes() method being used in the example. I will cover this next time. Over and out for now.