Section 1.1: TIL: Defining String Patterns with TypeScript

This month, I discovered how to utilize template literals in TypeScript to define specific string patterns:

type MetamaskChainId = 0x${string};

// ❌ Error: Type "123" is not assignable to type '0x${string}'

const id: MetamaskChainId = "123";

// ✅

const id: MetamaskChainId = "0x123";

Template literal types, introduced in TypeScript 4.1 (I know, it has been around for a while, but I still enjoy uncovering established features! 😉), allow us to create more precise type definitions. In the example above, MetamaskChainId is a type that requires a string to start with "0x". While TypeScript performs checks at compile time, it’s crucial to remember that these validations don’t occur at runtime. This feature isn't a fail-safe solution for type safety, but it significantly enhances code descriptiveness and usage guidance—especially with an IDE that supports IntelliSense.

Section 1.2: TIL: Accessing WASM Metadata in Node.js

This month, I stumbled upon a valuable technique: reading a canister's WebAssembly (WASM) module metadata section using Node.js. This insight proved beneficial, particularly in the context of Juno's new Serverless Function feature, where comprehending developer-added extensions to smart contracts is vital.

Accessing this metadata is quite simple:

const { readFileSync } = require('node:fs');

const wasmBuffer = readFileSync("/path/to/satellite.wasm");

const mod = new WebAssembly.Module(wasmBuffer);

const metadata =

WebAssembly.Module.customSections(mod, "icp:public juno:build");

const decoder = new TextDecoder();

const buildType = decoder.decode(metadata[0]);

console.log(buildType);

To retrieve the metadata from our WebAssembly (WASM), we inspect its custom sections. A WASM module consists of various sections, most of which conform to the WASM specification. However, developers can add custom sections that are ignored during standard validation. These custom sections enable the embedding of additional data within WASM modules. For example, the name custom section allows developers to assign names to all functions and locals within the module, similar to "symbols" in a native build.

In this context, we instantiate a WebAssembly.Module using a locally stored WASM file. We then extract the custom sections, focusing on the first one, as there is no additional metadata in this example.