Chapter 1
WebAssembly Fundamentals

With WebAssembly, there is a symbiotic relationship between the compiled WebAssembly binary (called a module) and the host responsible for interpreting it. This relationship is at the heart of everything that you can do with this new technology, and understanding where the boundaries are between module and host is key to being able to build effective WebAssembly applications.

WebAssembly can be viewed at two different levels—the raw, foundational level and at the higher level of other programming languages using WebAssembly as a target. Before you can understand and appreciate what languages like Rust are doing when they produce WebAssembly modules, you’ll need to know what WebAssembly can do, what it can’t, and how to use language-independent tools.

This chapter gets you started at the foundation level, giving you an overview of what WebAssembly is, how it works, and how other features can be built upon this foundation. By the end of this chapter, you’ll be able to create and build your own WebAssembly modules using cross-platform language tools and your favorite code editor. While what you learn in these first few chapters may not be things you do on a daily basis, the context they provide will be invaluable as you build real applications with WebAssembly.