Recent content on Learn ClojureScript
Lesson 30: Capstone 5 - Notes In this section, we have been learning how to use the Reagent framework to apply our ClojureScript knowledge to web applications. In this final capstone lesson, we will once again use a project to synthesize what we have learned about Reagent and modular application design. As in the previous capstone lessons, this one will draw on all that we have learned so far -…
Lesson 29: Separate Concerns Two broad strategies can be used when building a Reagent application. The first is to keep all state in a single atom, which is the approach that we used in the last lesson. The second is to keep different pieces of state separate and to use asynchronous communication between them. The first approach is simpler and easier to reason about, but the second is useful in…
Lesson 28: Using React via Reagent We have seen that React is a good platform for writing ClojureScript applications, but we have not yet written any code. While it is entirely possible to use the React API directly, we are going to be using Reagent, which provides a very simple API that lets us concern ourselves with writing components rather than fiddling with React lifecycle and complex state…
Lesson 27: React as a Platform In contrast to JavaScript’s multi-paradigm nature, ClojureScript promises a functional programming experience. However, we have found that as soon as we need to interact with the DOM, our code becomes… less than functional. In this lesson, we will explore how React’s declarative nature makes it a perfect platform for ClojureScript applications. We…
Lesson 26: Capstone 4 - Group Chat Congratulations! At this point, we have learned enough ClojureScript to write pretty much any sort of app that we would like. Sure, over the coming chapters, we will pick up some tools and techniques that will make us more productive, but nothing is stopping us from writing complete, production-quality apps with what we have learned so far. For this capstone, we…
Lesson 25: Intro to Core Async Asynchronous programming lives at the heart of web development. Almost every app needs to communicate with an API backend, respond to user input, or perform some other IO task without blocking the main thread. While it is entirely possible to use JavaScript’s Promise API from ClojureScript, we have another paradigm for asynchronous programming at our disposal -…
Lesson 24: Handling Exceptions and Errors We would like to think of programming as an idealized discipline where we write our programs declaratively and the computer converts them into pure computational models that can churn away until the heat death of the universe. In practice, bad things will happen, and they will happen much sooner than the heat death of the universe. Networks fail, we divide…
Lesson 22: Managing State This lesson has been a long time coming, and it is a critical one. By this point, we have seen that it is possible to write whole applications without using any mutable data, but for most cases, it is inconvenient to say the least. As we learned in the last lesson, ClojureScript encourages writing programs as a purely functional core surrounded by side-effecting code, and…
Lesson 23: Namespaces and Program Structure In ClojureScript, the unit of modularity is the namespace. A namespace is simply a logical grouping of functions and data that can be required and used by another namespace. External libraries expose modules as namespaces that we can require in our code, and we can (and should) break our code into multiple modules as well. In this lesson, we’ll…
Lesson 19: Mastering Data With Maps and Vectors In this lesson, we will explore some of the features of ClojureScript that make it simple to work with data. ClojureScript places a strong emphasis on relying on generic collection types and the standard functions that operate on them rather than creating highly specialized functions that only work on a single type of object. The object-oriented…
Lesson 18: Summarizing Data So far we have learned some useful operations that we can perform over sequences: map for transforming each element filter for selecting certain elements into for converting between collection types There is a lot that we can do with just these few functions. In fact, we rarely need to use something like a for loop with these functions at our disposal. In the last…
Lesson 17: Discovering Sequence Operations Programming is all about abstractions. The entire field of software engineering is devoted to making programs and systems that are better for human beings to reason about and maintain. The key to making clear and accurate systems is found in the concept of abstraction, which is identifying patterns that recur often and generalizing them to something that…
Lesson 16: Grokking Collections So far, we have been working with simple data types - strings, numbers, keywords, and the like. We saw a few collections when we took our survey of ClojureScript’s syntax, but we glossed over exactly what they are and how to use them in real applications. As we might imagine, writing programs without any way to represent data that belongs together would be…
Lesson 15: Capstone 2 - Temperature Converter Over the past few lessons, we have learned the basic concepts that we will need for practically any app that we write: variables for hanging on to values that we want to re-use, control structures for determining which code path should be taken, functions for defining re-usable behavior and calculations, and IO for interacting with the user. While…
Lesson 14: Performing I/O Web applications are all about interaction. Whether it is a form to gather simple input or animated charts, almost everything that we as web developers do is about either getting data from users or displaying data to them. Considering how important I/O is to every web application, we will look at it as our next “building block.” In this lesson: Get user input…
Lesson 20: Capstone 3 - Contact Book Over the past few lessons, we have learned the core tools for working with data in ClojureScript. First, we learned about the basic collection types - lists, vectors, maps, and sets - as well as the most common functions for working with these collections. Then we took a closer look at the important sequence abstraction that allows us to operate on all sorts of…
Lesson 21: Functional Programming Concepts ClojureScript sits at the intersection of functional programming and pragmatism. In this lesson, we will take a deeper look at what it means to be a functional language. As we shall see, functional programming is about much more than simply being able to use functions as values. At its core, the more important concepts are composability, functional…
Lesson 13: Interacting With JavaScript Data One of the advantages of ClojureScript is its excellent interoperability with JavaScript. When Clojure was first introduced, one of its primary goals was providing simple integration with existing Java code. ClojureScript continues in this spirit of valuing integration with its host platform. We will deal with JavaScript interoperability to a greater…
Lesson 12: Reusing Code With Functions ClojureScript is a functional programming language. The functional programming paradigm gives us superpowers, but - love it or hate it - it also makes certain demands on the way that we write code. We have already discussed some of the implications of functional code (immutable data, minimizing side effects, etc.), but up to this point we have not studied…
Learn ClojureScript: Table of Contents Section 0: Why ClojureScript Matters Lesson 1: A First Look Introducing ClojureScript ClojureScript’s Sweet Spots ClojureScript 101 Summary Lesson 2: ClojureScript in the JavaScript Ecosystem Why JavaScript Needs Clojure Why Clojure Needs JavaScript Summary Lesson 3: Building Blocks Parens, Parens Everywhere! Core Data Types Summary Lesson 4:…
Lesson 7: REPL Crash Course In the previous lesson, we learned how to use Figwheel to reload code whenever a source file changed, enabling a very quick feedback cycle. In this lesson, we will take a first look into a tool called a REPL, which stands for Read-Eval-Print Loop and is conceptually similar to the JavaScript console that most browsers provide. While live reloading is a great help when…
Lesson 11: Looping In the last lesson, we looked at ClojureScript’s versions of we usually call branching control structure. However, we learned that things work a little bit different in ClojureScript compared to other languages that we may be used to - control structures are expressions rather than imperative controls. Now as we come to another fundamental topic - loops - we will learn…
Lesson 10: Making Choices Up to this point, we have mostly been writing code that has some starting point and progresses until it is complete.1 It has a well-defined task and must follow a well-defined series of instructions to accomplish this task. What we have been missing is the concept of a choice - being able to take a different path depending on some condition. Imagine a road that stretched…
Lesson 9: Using Variables and Values ClojureScript takes what we think we know about variables and turns it on its head. Instead of thinking about variables that may be modified, we should start thinking about values that cannot be changed. While ClojureScript has the concept of a variable (called a var), we cannot usually change that value that a variable refers to. ClojureScript is careful to…
Lesson 8: Capstone 1 - Weather Forecasting App Over the past couple of lessons, we have been getting familiar with the most common tools for the ClojureScript developer. While we have written a smattering of code, the focus has been on the project itself. This lesson will change course slightly and focus on writing a minimal app. This lesson will be a bit more difficult, and we will gloss over…
Lesson 6: Receiving Rapid Feedback With Figwheel In the last lesson, we only executed one command, but we already have a basic project that will compile, and as we will see in a moment, automatically reload. Figwheel is the tool of choice in the ClojureScript community for reloading code and executing ClojureScript inside a web browser. Interactive development has been a huge priority for…
Lesson 5: Bootstrapping a ClojureScript Project Until this point, our discussion of ClojureScript has been largely theoretical. We have an idea of why we would want to use ClojureScript, but what does it look like in action? Over the course of this section, we’ll develop a small weather forecasting application from scratch. We will pay attention to the high-level concepts while leaving the…
Lesson 4: Expressions and Evaluation As we briefly touched on in the previous lesson, the concept of an expression is at the core of ClojureScript code. For programmers coming from a language like JavaScript, thinking in terms of expressions requires a shift in perspective, but like most aspects of ClojureScript, we will find that programming with expressions is quite simple once we get used to…
Lesson 3: Building Blocks With an understanding of what ClojureScript is and why it matters, we will begin our journey with an overview of the basics of the language. One of the biggest hurdles in learning an unfamiliar language is understanding the syntax. While there is a great deal of crossover between languages at the conceptual level, the way that those concepts are expressed can be quite…
Lesson 1: A First Look In today’s technology landscape, the web is king. Web apps are everywhere, and the lingua franca of the web is JavaScript. Whether the task is adding interactivity to a simple web page, creating a complex single-page application, or even writing microservices, JavaScript is the defacto tool. Despite its age, JavaScript has evolved to power an entire generation of web…
Lesson 2: ClojureScript in the JavaScript Ecosystem Now that we have a good idea of what ClojureScript is and how to use it, we will continue to pull back the curtain to get a clearer picture of how this curious language fits into its environment - the JavaScript ecosystem. While the language is quite different from JavaScript, it maintains a symbiotic relationship to its JavaScript host.…