Function Composition in JavaScript

Introduction

In this lab, we will explore the concept of function composition in JavaScript. We will learn how to combine multiple functions to create a new function, and how to use the compose() function to perform right-to-left function composition. Through hands-on examples and exercises, we will gain a deeper understanding of this powerful technique and its practical applications in programming.

Skills Graph

How to Compose Functions in JavaScript

To start practicing coding using function composition in JavaScript, open the Terminal/SSH and type node.

Here's an example of how to perform right-to-left function composition in JavaScript:

1. Use Array.prototype.reduce() to perform right-to-left function composition.
2. The last (rightmost) function can accept one or more arguments; the remaining functions must be unary.
3. Define the compose function that will take any number of functions as arguments and return a new function that composes them.
4. Call the compose function with the desired functions in the desired order.
5. Call the new composed function with any necessary arguments.

const compose = (...fns) =>
  fns.reduce(
    (f, g) =>
      (...args) =>
        f(g(...args))
  );

For example, let's say we have two functions:

const add5 = (x) => x + 5;
const multiply = (x, y) => x * y;

We can compose these functions using compose:

const multiplyAndAdd5 = compose(add5, multiply);

Now we can call multiplyAndAdd5 with the desired arguments:

multiplyAndAdd5(5, 2); // 15

Summary

Congratulations! You have completed the Compose Functions lab. You can practice more labs in LabEx to improve your skills.