Book excerpt: A fast paced guide for JavaScript developers for writing safe, fast, and reusable code by leveraging ResaonML's strong static type system Key FeaturesReduce code errors with the power of type systemsEmploy static typechecking and genericity to promote code reuse and consistencyUnderstand functional programming which is the foundation of type-driven developmentBook Description Type-driven development is an approach that uses a static type system to achieve results including safety and efficiency. Types are used to express relationships and other assumptions directly in the code, and these assumptions are enforced by the compiler before the code is run. Learn Type-Driven Development covers how to use these type systems to check the logical consistency of your code. This book begins with the basic idea behind type-driven development. You’ll learn about values (or terms) and how they contrast with types. As you progress through the chapters, you’ll cover how to combine types and values inside modules and build structured types out of simpler ones. You’ll then understand how to express choices or alternatives directly in the type system using variants, polymorphic variants, and generalized algebraic data types. You’ll also get to grips with sum types, build sophisticated data types from generics, and explore functions that express change in the types of values. In the concluding chapters, you’ll cover advanced techniques for code reuse, such as parametric polymorphism and subtyping. By end of this book, you will have learned how to iterate through a type-driven process of solving coding problems using static types, together with dynamic behavior, to obtain more safety and speed. What you will learnUse static types to capture information, making programs safer and faster Learn ReasonML from experienced type-driven developers Enhance safety by simply using basic types Understand the most important type-driven concepts with simple examples Explore a design space using static typing and find the best way to express your system rules Use static types and dynamic runtime in harmony to write even safer and faster codeWho this book is for If you’re a programmer working with dynamically typed languages and are looking for ways to mitigate production runtime errors, Learn Type-Driven Development is for you. You’ll also find this book helpful if you’re a programmer working with statically typed languages looking for increased safety and improved performance.