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WASM TLDR - What is WASM, and why is it important?

WebAssembly (Wasm) is becoming a core part of many technology stacks. It is a portable target for higher-level languages to compile to and has no direct limitations on where it can run (although it is mostly browser focused at the moment). It can run at near-native speeds and provides a sandboxed, agnostic set of instructions to run in any environment that supports it.

Wasm has two standard formats, .wat and .wasm.

  • .wat - a text-based format called WebAssembly Text, a more human-readable way of representing Wasm instructions.
  • .wasm - a binary-based format that defines an executable that is then executed by a Wasm virtual machine.

WebAssembly, while not exclusive to Rust by any means, is highly supported by Rust. This enables Rust code to be even more portable in web-based applications (or any environment that supports WebAssembly).

Forkless Upgrades, thanks to WASM

Heard of forkless upgrades on Polkadot? It is Wasm that enables these seamless blockchain upgrades. Each instance of the Polkadot Runtime compiles to a Wasm blob and is stored in the blockchain's storage, which can be replaced through an on-chain governance-based upgrade.

Basic Wasm Architecture​

At its core, Wasm is a stack-based virtual machine where each value is pulled and pushed on an arbitrary stack. It is worth noting that Wasm is not a register machine, as it contains no context-specific registers for holding bytes.

Wasm Use cases​

On Polkadot, Wasm is a core part of the technology stack:

  • It defines reliable state transition functions for the relay chain runtimes.
  • It defines Parachain Validation Functions (PVFs), which is a core part of how relay and parachains agree on their respective state.
  • The ink! smart contract language compiles to Wasm, which takes full advantage of Wasm’s sandboxed and portable nature.