In this article, we will learn about declarative pattern, pure function, Immutability and side effects. Refer this github repo for the usage of above methods A function in JavaScript can be defined in the following way: function (param1, param2, ...){ /* body */}; Or in ECMAScript 6, in the following way: Even though functional programming can vastly improve an application’s code, its principles can prove a bit challenging at first. Functions In JavaScript. It means that a program can be designed to read, generate, analyze or transform other programs, and even modify itself while running. Just like the OOP approach, this approach can be an overkill for very simply use-cases (like the example above) but it can really shine in more complex applications. So which approach is best, which approach should you use? Of course this is a bit of a redundant function but you could do more in there than just select an element. It’s pretty straightforward vanilla JavaScript code. Now, let’s imagine we want to calculate a product’s price, taking into account VAT and possible discounts. The advantage of the functional approach is that you have a bunch of highly re-usable (and managable) functions which have little to no extra dependencies. Things started to change for JavaScript since then and Functional Programming in Front-End web development were starting to have its appeal thanks to those frameworks. In this article, we will learn about declarative pattern, pure function, Immutability and side effects. There are libraries which can help us to achieve the immutability. Here, second approach is Functional Programming where filter() method takes care of “how program operates” and program focuses only on input i.e. It’s up to you which approach you prefer. This might be hard for some religious fanatics out there but if it works for you (and your team), you can of course go with such a hybrid style as well. Created by Maximilian SchwarzmüllerLast Updated on December 18, 2019. Functional Programming treats computation as the evaluation of mathematical functions. New libraries and frameworks appear at a frantic pace, offering new architectures and functionalities. //we calculate the final price of a product that’s worth 25, with 21% VAT and a 10% discount. Because JavaScript is a lan-guage I’m very much obsessed with, to say the least, I was thrilled to jump into this opportunity. If we would follow an object-oriented style, we could re-write (and arguably over-engineer this simple example) in the following way: As mentioned: This is definitely over-engineered. Apparently, it was React which encourages functional-based design when using their library since it enforces you not to mutate your objects and not introduce side-effects as well. As always, share any feedback you have! These three approaches will be shown at the example of JavaScript but they apply for most programming languages (some languages push you towards a certain paradigm though - JavaScript doesn’t). This makes your code very easy to maintain and understand. There are libraries which provide utility functions to make code more declarative. Your data is stored in properties, your logic in methods. The only inconvenient would be the initial barrier we need to overcome, but that can be done watching some examples and doing some tests. //Instead of returning the default value in the else: //getOrElse will either return someuser’s valuer or the default value that we specified. By writing this book, I hope to help you develop the same skills and take your development in a new direction. And properties and methods that work closely together live in the same class. The video on top of the page already shows a bit of a better example (i.e. Opinions expressed by DZone contributors are their own. Of course there also are mixed approaches - you can build an app where you use some classes and some functions (outside of classes). Let’s see an implementation of the ‘getGreetingForUser’ function following an imperative model: As you can see, we had to check if the user already existed, if he/she had a language set and if said language is among the ones that have a welcome message prepared. Concepts and Terms that Every Software Engineer Needs to Know, Understanding Destructuring, Rest Parameters and Spread Syntax, Building a Simple Web App Using the Observer Pattern, In computer science, functional programming is a programming paradigm or pattern (a style of building the structure and elements of computer programs). We hope that with this article you can start to explore the Functional Programming in JavaScript and/or in any language you work with. "Discounts not available for low-priced items". Sometimes, side-effects can’t be avoided (and this is okay) but you should aim for functions that take some input (=> parameters) and produce/ return a reliable output. The program is having side effect because the actual responsibility of function scheduleMeetup is to add the date and place of the meetup but it’s modifying the value of isActive as well on which some other function publishMeetup is depended upon and as a side effect the publishMeetup function will not have desired output because it’s input has changed in between. Here’s the same example one more time - again over-engineered. There, we build a simple dummy website three times - once with each approach.

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