Learning React, 3rd Edition

Chapter 3. Functional Programming with JavaScript

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When you start to explore React, you’ll likely notice that the topic of functional programming comes up a lot. Functional techniques are being used more and more in JavaScript projects, particularly React projects.

It’s likely that you’ve already written functional JavaScript code without thinking about it. If you’ve mapped or reduced an array, then you’re already on your way to becoming a functional JavaScript programmer. Functional programming techniques are core not only to React but to many of the libraries in the React ecosystem as well.

If you’re wondering where this functional trend came from, the answer is the 1930s, with the invention of lambda calculus, or λ-calculus.¹ Functions have been a part of calculus since it emerged in the 17th century. Functions can be sent to functions as arguments or returned from functions as results.  More complex functions, called higher-order functions, can manipulate functions and use them as either ...