WebAssembly was designed for the browser but has found a second home on the server. WASM outside the browser promises portable, sandboxed, near-native performance computation. The ecosystem is still maturing but the trajectory is clear.
Why WASM beyond the browser
WebAssembly's value proposition outside the browser is: portability (compile once, run anywhere that has a WASM runtime), sandboxing (untrusted code can run in a WASM sandbox with limited capabilities), and near-native performance (WASM executes at close to native speed without a JIT). These properties are interesting for plugin architectures, edge compute, and serverless functions.
The WASI standard
WASM System Interface (WASI) defines how WASM modules interact with the host operating system: file access, network sockets, clocks. Without WASI, a WASM module cannot do anything outside its sandbox. With WASI, it can interact with the system through a controlled interface. WASI 0.2, released as a stable standard in 2023, is the foundation for server-side WASM deployment.
Fermyon and the WASM app platform
Fermyon Spin is an open source framework for building microservices in WASM. You write a function in Rust, Go, or Python, compile to WASM, and deploy with Spin. The startup time is under 1 millisecond (versus 100-200ms for containers). The isolation is stronger than container isolation. The use case is for serverless functions and microservices where cold start latency is a concern.
The.NET WASM story
Microsoft's Blazor WebAssembly runs.NET applications in the browser via WASM. For server-side WASM,.NET 8 and the NativeAOT-based WASM runtime are on the roadmap. The.NET WASM story outside the browser is less mature than Rust's, but the direction is clear:.NET code compiled to WASM for edge and serverless scenarios.