Learn functional programming in JavaScript

JavaScript is one of the coolest programming languages, simply because you can write software in a variety of different ways. We mostly live in an object-oriented world, but we are not locked into that paradigm. We can also take a functional programming approach.

1. What you will learn in this free JavaScript course

Watch the video lesson [0:00:00] ↗

By the end of this course, you will understand concepts such as:

• first-class functions
• immutability
• compositional functions
• curry
• how to work with the DOM functionally

Setting up

Watch the video lesson [0:01:53] ↗

Let’s prep our development area and get it ready for coding! In this lesson I will show you how.

To configure JavaScript and our working environment, we will use the following tools:

2. Basic concepts

First-class functions

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In JavaScript, functions are first-class objects. They are a data type that we can assign to variables, pass to other functions, and even return functions from within another function. It’s a powerful feature and is critical to functional programming.

Declarative programming

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Functional programming takes a declarative approach to writing code. It’s a common (and very trendy) way to write code. We will look at declarative programming and compare it to imperative programming in this lesson.

Pure and impure functions

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There are two types of functions in functional programming: pure and impure. You will learn the difference between the two in this lesson.

Immutability

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We usually work with immutable data in functional programming. It may seem like more work to program immutably and inefficiently to boot, but there are benefits to using immutable data. You will learn why in this lesson.

3. Build a functional project

Presentation of the composition

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A key aspect of functional programming is the concept of composition: composing multiple functions into one. You will learn about the two types of composition in this lesson.

Using composition

Watch the video lesson [00:34:28] ↗

Now that you know the composition types, we’ll compose multiple functions together to create an HTML element.

Curry features

Watch the video lesson [00:41:11] ↗

Curry may be a difficult concept to grasp at first, but it is extremely powerful and allows us to create partial functions.

Write a functional web app

Watch the video lesson [00:48:12] ↗

Most of the code we’ve written just creates helper functions. In this lesson, we’ll start writing application code to display messages on the page.

Event management

Watch the video lesson [00:56:53] ↗

Handling events in a functional way is not much different than the procedural way, except that we now take care of our event configuration functions. I’ll show you how to do it so you can complete our application in this lesson.

For further reading:

4. Working with arrays

Comprehension map()

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One of the most useful and underused operations in all of programming is the idea of ​​a map, i.e. transforming one array into another array. I’ll show you how to do it with JavaScript map() method.

Filter arrays

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It’s very common to want to filter an array into a smaller data set. In this lesson you will learn how with the filter() method.

Reduction matrices

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THE reduce() operation is very useful and you will learn how it works and how to apply it in this lesson.

For more insights into this topic, check out these two articles:

Conclusion

Watch the video lesson [1:32:15] ↗