Fundamentals of WebAssembly: Modules, Binary and Text Formats

The article begins with an overview of WebAssembly, its key features, history, and typical use cases, then moves to the basic concepts of modules, types, variables, functions, instructions, traps, tables, and linear memory.

It explains that a module is the fundamental unit containing functions, memory, globals, and tables, and describes how a module is instantiated into an instance via WebAssembly.instantiate or new WebAssembly.Instance .

Fourteen‑byte variable types ( i32 , i64 , f32 , f64 ) and extended types such as v128 , funcref , and externref are introduced, along with their signed/unsigned variants.

The binary module structure is detailed, listing the twelve optional sections (custom, type, function, table, memory, global, import, export, start, element, code, data, data‑count) and showing how they must appear in a fixed order after the four‑byte magic number and version.

For the text format, the article describes the S‑expression syntax, lexical tokens (integers, floats, strings, names, identifiers), and the various type definitions used in the textual representation.

Several concrete code snippets illustrate the syntax, for example a minimal module and a function definition:

(module (func $add (param $lhs i32) (param $rhs i32) (result i32) get_local $lhs get_local $rhs i32.add))

It also shows how to declare imports, exports, memories, data segments, globals, tables, element segments, and a start function, and provides a complete example that builds a simple module, compiles it with wat2wasm , and invokes it from JavaScript.

The concluding section summarizes that the WebAssembly binary and text formats are closely related, encourages readers to experiment with hand‑written modules, and points to further resources.