JavaScript Functional Programming: Benefits & Best Practices

Functional programming is a style of software development that focuses on the use of functions to structure and optimize code. JavaScript has grown in popularity as a language for functional programming, allowing developers to unlock numerous possibilities. In this blog post, we will delve into the benefits of using JavaScript for functional programming, while supporting good coding practices that keep code clean and understandable. Follow these suggestions and you will be able to take advantage of the many advantages offered by functional programming.

Understanding the Basics of Functional Programming

There are various paradigms that programmers might use when writing code.
Functional programming, a declarative programming paradigm, is one of them.

Immutable data structures and function evaluation are the cornerstones of functional programming.
This indicates that programmers who use the functional programming approach strive to design code that is simple to reason about and comprehend.

How Functional Programming In JavaScript Differs

Imperative programming involves writing code that is executed sequentially, whereas functional programming is focused on the evaluation of functions. In JavaScript, this means writing code that uses pure functions, avoids side effects, and utilizes higher-order functions like map and reduce.

Functional ProgrammingImperative Programming
Focuses on what to do, not how to do it.Focuses on how to do things, step by step.
Functions are pure, meaning they don’t have side effects.Functions can have side effects, which means they can change the state of the program.
Functional programs are easier to reason about and test.Imperative programs are more efficient and can be used to control the flow of execution more precisely.
Functional programming is often used for data analysis and machine learning.Imperative programming is often used for system programming and game development.

Using a functional programming strategy has several advantages, such as:

Benefits of functional programming in JavaScript

  1. Improved code quality: By using functions as the basic building blocks of your code, you’ll write cleaner, more maintainable code.
  2. Better code reusability: Functions are reusable, making it easier to share code across different parts of your application.
  3. Easier testing: Functions are easier to test because they have a single responsibility, making it easier to isolate and verify their behavior.
  4. Improved performance: Functions in Javascript are optimized for performance, so using functional programming techniques can lead to faster code execution.
  5. Improved code collaboration: Functions are easy to understand, making it easier for multiple developers to work on the same codebase.

Best practices for applying functional programming in JavaScript

Embrace immutability

In functional programming, values are immutable, meaning they cannot be changed once they are set. This leads to less side effects, improved code quality, and easier testing. Data structures used in functional programming are frequently immutable. This results in higher-quality code with fewer problems.

Avoid side effects

Side effects are any changes to state or output outside of the function. Avoiding side effects leads to more predictable and maintainable code.

Avoid mutating data

Mutating data can lead to unanticipated side effects in your code, making it more difficult to debug and understand. Instead, aim to use immutable data structures whenever possible. In functional programming, this could mean using functions like `map` and `filter` instead of `for` loops that directly modify an array.  You should avoid changing the state of your data. Instead, you should create new objects with the updated state. This is called immutability. This makes your code more predictable and easier to test. You can use libraries like Immutable.js or Ramda to help you with this.

Use callbacks & Promises

Callbacks and Promises are used in functional programming to ensure that certain actions occur after a certain event has taken place. Callbacks are functions that are called after a specific action has been completed, while Promises are objects that represent the eventual completion of an asynchronous operation. They are used to ensure that certain tasks are executed after a certain event has occurred, allowing for a more structured and organized approach to programming. An example would be a website requires a user to log in before they can access content. A callback function could be used to allow the user access once the login process is complete.

And of course promises are heavily used in making API requests. For example, a web service is making an API request for data from an external server. A Promise object could be used to ensure that the data is returned and processed once the response from the server is received.

The useCallback hook is a React hook that allows developers to create a callback function that can be reused in a functional component. It can be used to ensure that certain actions are executed after specific events have occurred, making it an ideal tool for achieving the same goals as those of callbacks and promises. We will discuss functional programming related to ReactJS in a bit.

Embrace composition

Functions in functional programming can be composed to create new functions. This leads to more maintainable and reusable code.

Avoid loops

Loops are often used to iterate over collections of data. In functional programming, loops are avoided in favor of using higher-order functions and recursion, again similar to arrow function these are ES6 features.

Functional Programming in ReactJS

ReactJS is one of the most popular JavaScript library for building user interfaces. It is based on the concept of components, which are reusable and composable units of code that represent a part of the user interface. ReactJS also embraces functional programming principles, making it a great choice for developers who want to incorporate functional programming into their workflow. It makes for much cleaner and easier to read code. There is also less code in general when working with functional components compared to classes.

function Welcome({name}) {
  return <h1>Hello, {name}</h1>;

In this example, the Welcome component is a pure function that takes in a props object and returns a tree of elements. This makes it easy to understand what the component does and how it should be used.

Immutable State in ReactJS

ReactJS encourages the use of immutability by default. This means that the state of a component should never be directly modified. Instead, new state should be created from the old state. This helps to eliminate the possibility of unexpected side effects and makes it easier to reason about the code.

const [count, setCount] = useState(0);

function handleClick() {
  setCount(count + 1);

In this example, the count state is never directly modified. Instead, the setCount function is used to create new state from the old state. This makes it easy to understand how the state is being changed and eliminates the possibility of unexpected side effects.

Higher-Order Components in ReactJS

Higher-order components are functions that take components as arguments or return components as values. In ReactJS, higher-order components can be used to add additional behavior to components, such as connecting to a data store or adding styles.

function withData(Component) {
  return function(props) {
    const data = fetchData();
    return <Component data={data} {...props} />;

const WelcomeWithData = withData(Welcome);

In this example, the withData higher-order component takes in a Component and returns a new component that fetches data and passes it as a prop to the original component. This allows developers to reuse the withData behavior across multiple components, making their code more modular and maintainable.

How is functional programming different from OOP?

  1. Philosophy:
  • Functional programming focuses on treating computation as the evaluation of mathematical functions and avoids changing state and mutable data.
  • OOP focuses on modeling real-world objects and the interactions between them, and uses encapsulation, inheritance, and polymorphism to manage complexity.
  1. Techniques:
  • Functional programming emphasizes immutability, pure functions, higher-order functions, and recursion.
  • OOP emphasizes encapsulation, classes, objects, and methods.
  1. Approach to solving problems:
  • Functional programming breaks down problems into smaller, independent functions that can be combined and re-used.
  • OOP breaks down problems into objects that represent real-world entities and encapsulate their behavior and state.

Ultimately, functional programming and OOP are two different approaches to software development that have different philosophies, techniques, and ways of solving problems. Both have their own strengths and weaknesses and can be used together in certain situations to achieve the best results.


Functional programming and ReactJS are a natural fit. By writing components as pure functions, embracing immutability, and utilizing higher-order components, developers can write code that is more maintainable, performant, and productive. So why not give it a try in your next ReactJS project?


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