What are Higher-order functions (HOF)? The benefits of using them in your projects.

The Problem

I still remember when I first read an article about Higher-order functions, there was a certain level of confusion. Being new to the field, the theoretical aspect was quite difficult to grasp. At that time, I understood the concept but couldn't visualize its practical applications. It took me a while to realize that this was something I had been using regularly all along!

There are already many articles about Higher-order functions on the internet, just search on Google and you will find them. However, because HOF is an important and highly applicable concept, I would like to write an article from a personal perspective. Without further ado, let's get started.

What are HOF?

Higher-order functions in JavaScript are functions that can take one or more functions as arguments or return another function.

For example, a function can be passed as an argument to another function, or a function can return another function to be used in our code. This allows us to create flexible and reusable functions.

In JavaScript, functions like map, filter, reduce… are typical examples of HOF. They all take a function as an argument and apply that function to an array or other values to perform a certain transformation.

How to use them

You can apply HOF to create flexible functions of your own or create reusable functions.

One of the common use cases for HOF is in functions like map, filter, reduce. If you are not familiar with the usefulness of these three functions, I have a detailed article on Why you should be proficient with the map, filter, and reduce trio in JavaScript?.

Back to the problem, let's say we have an array and we need to apply an operation to all elements in it, then we use map.

const arr = [1, 2, 3];
const arr2 = arr.map(function (item) {
  return item + 1;
});

map is an HOF because it takes a function as a parameter. As the parameter is a function, we can rewrite the above code in a reusable way like this:

const addOne = a => a + 1;

const arr = [1, 2, 3];
const arr2 = arr.map(addOne);

addOne is a function that takes a number a and returns a + 1. Thus, we can use addOne in multiple map functions without the need to rewrite the addition logic.

Benefits of HOF

HOF brings many benefits in programming:

• Reusability: HOF allows creating flexible and reusable functions to solve various problems without rewriting the same code multiple times. It reduces code duplication.

• Separation of data and logic, simplifying code writing: HOF allows separating data and logic, making the code more readable and maintainable. In the example above, instead of guessing what map is doing, we can just look at the function name addOne to get an idea.

• Many HOF functions are created to support programming. Examples include map, filter, and many others. They are designed to save coding time, as without them, you would have to write more code to achieve the same purpose. In addition, there are many HOF functions in asynchronous processing like Promise, async/await, and application libraries that provide flexible processing functions for developers.

Along with the benefits, HOF can be difficult to understand and access for beginners in JavaScript, but this problem can be overcome with time. Additionally, using too many HOF functions can introduce a certain level of complexity in code comprehension and maintenance (each function is an object created), or for future maintenance. However, these weaknesses can be completely overcome with time and experience gained by programmers.

Conclusion

Higher-order functions (HOF) are functions that can take functions or return a function. HOF is widely used in JavaScript programming because of the benefits it provides. However, it can also cause difficulties in understanding for beginners and potential maintenance issues.