The WebAssembly Component Model defines a standard interface system enabling cross-language composition beyond numeric values. Understanding WIT interface definitions, WASI 0.2, resource types, and toolchains like jco is essential for the next generation of portable, polyglot Wasm applications.
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What problem does the WebAssembly Component Model solve that core Wasm modules do not?
Core Wasm only passes numbers between modules. The Component Model defines a type system (strings, lists, records, variants, resources) and ABI so components written in different languages can safely call each other using rich types without hand-written glue code.
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In the Component Model, what is a WIT (Wasm Interface Type) file?
WIT is the IDL for the Component Model. It defines interface and world blocks describing what a component provides and requires. Toolchains (like wit-bindgen) generate host and guest bindings from WIT, automating the ABI glue.
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What is WASI 0.2 (the WebAssembly System Interface Preview 2)?
WASI 0.2 is the first stable WASI spec built entirely on the Component Model. It replaces the older POSIX-style imports with WIT-defined interfaces (wasi:io, wasi:http, etc.), enabling components to be portable across runtimes that implement the same WASI world.
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What does the jco toolchain provide in the WebAssembly Component Model ecosystem?
jco is the JavaScript Component Model toolchain. It transpiles .wasm components to JavaScript ES modules (for browsers and Deno) and generates TypeScript bindings from WIT files. It is the primary path for running WASI 0.2 components in JavaScript environments.
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The Component Model's resource type represents a handle to an opaque object. Why is this important for safe cross-language composition?
Resources are an abstraction for objects with identity and lifecycle. A component can pass a resource handle (an opaque integer) to another component without sharing raw memory pointers. The Component Model type system distinguishes owned handles (caller takes responsibility) from borrowed ones (caller cannot outlive the lender), ensuring safety.