In Chapter 1, What is WebAssembly?, we talked about how the binary and text formats of WebAssembly both map to a common structure in the form of an abstract syntax. Before getting into the nuts and bolts of these formats, it's worth mentioning how these are related within the Core Specification. The following diagram is a visual representation of the table of contents (with some sections excluded for clarity):

As you can see, the Text Format and Binary Format sections contain subsections for Values, Types, Instructions, and Modules that correlate with the Structure section. Consequently, much of what we cover in the next section for the text format have direct corollaries with the binary format. With that in mind, let's dive into the text format.

The Text Format section of the Core Specification provides technical descriptions for common language concepts such as values, types, and instructions. These are important concepts to know and understand if you're planning on building tooling for WebAssembly, but not necessary if you just plan on using it in your applications. That being said, the text format is an important part of WebAssembly, so there are concepts you should be aware of. In this section, we will dig into some of the details of the text format and highlight important points from the Core Specification.

To understand Wat, let's start with the first sentence of the description taken directly from the WebAssembly...

The Binary Format section of the Core Specification provides the same level of detail with regard to language concepts as the Text format section. In this section, we will briefly cover some high-level details about the binary format and discuss the various sections that make up a Wasm module.

The binary format is defined as a dense linear encoding of the abstract syntax. Without getting too technical, that essentially means it's an efficient form of binary that allows for fast decoding, small file size, and reduced memory usage. The file representation of the binary format is a .wasm file, which will be the compilation output from Emscripten...

In addition to the WebAssembly Core Specification, there are two API specifications for interacting with WebAssembly modules: the WebAssembly JavaScript Interface (JavaScript API) and the WebAssembly Web API. In the previous sections, we covered pertinent aspects of the Core Specification to become familiar with the underlying technology. If you never read the Core Specification (or if you skipped the first few sections of this chapter), it wouldn't inhibit the use of WebAssembly in your application. That is not the case for the APIs, as they describe the methods and interface required to instantiate and interact with your compiled Wasm module. In this section, we will review the Web and JavaScript APIs and describe how to load and communicate with a Wasm module using JavaScript.

We spent this chapter reviewing the various elements of WebAssembly and the corresponding JavaScript and Web APIs, but understanding how the pieces fit together can still be confusing. As we progress through the examples in this book and you're able to see how C/C++, WebAssembly, and JavaScript interact, these concepts will become clearer.

That being said, a demonstration of this interaction may help in clearing up some of the confusion. In this section, we're going to use an online tool called WasmFiddle to demonstrate the relationship between these elements so you can see WebAssembly in action and get a high-level overview of the development workflow.

WasmFiddle...

In this chapter, we discussed the elements of WebAssembly and their relationship. The structure of the Core Specification was used to describe the mapping of the text and binary formats to a common abstract syntax. We highlighted aspects of the text format (Wat) that can be useful in the context of debugging and development, as well as why s-expressions are an excellent fit for the textual representation of the abstract syntax. We also reviewed details pertaining to the binary format and the various elements that make up a module. The methods and objects within the JavaScript and Web APIs were defined with descriptions of their roles with regard to WebAssembly interaction. Finally, a simple example of the relationship between source code, Wat, and JavaScript was presented using the WasmFiddle tool. 

In Chapter 3, Setting Up a Development Environment, we&apos...

1. What kind of data are s-expressions good at representing?
2. What are the four language concepts that are shared between the binary and text formats?
3. What is one of the use cases for the text format?
4. What is the only element type that can be stored in a WebAssembly Table?
5. What does the JavaScript engine use to manage execution?
6. Which method requires less code to instantiate a module, instantiate() or instantiateStreaming()?
7. What error objects are available on the WebAssembly JavaScript object and what event causes each one?