JS: forEach, map, reduce, filter & sort overview

These 5 functions have become a staple of working with arrays in JS since they were introduced.

Here's a quick overview of what each one does and how we can use them. 1/8
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Before diving into the list, I wanted to cover what allows all of these functions to exist. They are all examples of 'Higher-Order Functions'.

This is when a function operates on another. I covered it further in the thread linked. 2/8

https://twitter.com/MrConerMurphy/status/1364206725826564109

.forEach()

.forEach() allows us to loop over an array and access each item individually, similar to how a for loop would do it but in a nicer syntax.

You can't return values from a .forEach() if you want to return values you need to use .map(). 3/8

.map()

As mentioned for .forEach(), if you want to iterate over an array, manipulate the value(s) in some way & return the final results, you need to use a .map()

.map() and .forEach() are very similar, to tell which to use think if you need to return a new array. 4/8

.reduce()

.reduce() is a special method that is often one of the hardest to learn due to how versatile it is.

With a .map() you operate on the values & return. But, with .reduce(), you can do pretty much anything.

In this example, I sum the values in the array. 5/8

.filter()

.filter() does what it says on the tin, it filters the array down to a smaller size based on if each value passes/fails the filter condition.

In this example, I check if the value is an even number by checking if the remainder of dividing by 2 is 0. 6/8

.sort()

.sort() allows us to sort an array based on a compare function we pass in.

Sort works by taking 2 values (a,b) and checking if one is larger than the other to ascertain the correct order. This is then returned as a new array. 7/8

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