Basically, any function that changes its inputs or the value of some external variable is an impure function. Templates let you quickly answer FAQs or store snippets for re-use. An imperative Javascript solution to this problem is something like: We say exactly what our function needs to do — iterate over the collection, compare the collection current item with x, and push this element to the resultArray if it pass the condition. Functional programming gives us some principles which make our code more readable, predictable and testable. Using reduce, we can build a function to handle the amount sum and pass it as an argument to the reduce function. Now imagine some mathematicians argue that the PI value is actually 42and change the value of the global object. Another interesting Hacker Rank problem was the update list problem. Is a PDF? Let's take a look at these. Our impure function receives that value and re-assigns the counter with the value increased by 1. Now we have an f argument, and use it to process a and b. If you’re using redux for your React-based projects, you’ll know what I mean. I hope you saw something useful to you here. You don’t need to worry about that because it’s not a bad thing. Thinking here now. Between two words when one is more specific, I choose the specific one unless I specifically want to generalize. No, it’s not. For example, the input [1 2 3 -4 5]needs the output to be [1 2 3 4 5]. The other point of consideration is that in some environments it is unavoidable to have mutations to the inputs and so clones and copies become the default solution to avoid mutation to the original values which this example showcases. A simple solution would be an in-place update for each collection value. And then the reduce combines all items by adding up. Beautiful! After a long time learning and working with object-oriented programming, I took a step back to think about system complexity. Fair enough, it’s a point though. You can make a tax-deductible donation here. Functional programming is a paradigm which has its roots in mathematics, primarily stemming from lambda calculus. Here we have imperative programming saying exactly what we want to do in each slugify process — first lower case, then remove useless white spaces and, finally, replace remaining white spaces with hyphens. My first idea was to build a to-absolute function to handle only one value. If we follow these two simple rules, it gets easier to understand our programs. Really doesn't matter. Thanks for the comments! The algorithm? We can replace the entire expression with a numerical constant and memoize it. In the following articles we will be looking at some functions which will help us develop more function driven applications. Yes, map can do it! That’s why in this example above, the change of finalPrice does not affect the value of totalPrice although we assign totalPrice to finalPrice in the first place. 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