Module Harmony

JSConf JP 2025
https://jsconf.jp/2025/

Transcript

1. Module Harmony JSConf JP 2025 pixiv Inc. 森内建太 @petamoriken 2025.11.16
2. 2 Self-Introduction • A Deno contributor • An advocate for ES2025 Float16Array • I like to keep up with Web Standards ◦ Sharing new stuff in the company's frontend community petamoriken pixiv WebDev engineer in Fukuoka
3. 3 https://scrapbox.io/petamoriken/
4. 4 好きな TC39 Proposals 発表ドラゴン ©ンバヂ https://x.com/nbaji9
5. 5 Table of Contents • ES Modules • Current Specification • Current Proposals ◦ Import Phase Modifiers ◦ Other Proposals • To conclude
6. ES Modules 6
7. 7 ES Modules import { foo } from "./foo.mjs"; import * as bar from "./bar.mjs"; import baz from "./baz.mjs"; import qux from "./qux.json" with { type: "json" }; export { foo } from "./foo.mjs"; const namespace = await import("./foo.mjs");
8. Current Specification 8
9. 9 ES Module Graph : Module Record
10. 10 ES Module Graph JS JS JS JS JSON JS JS * * ESM Integration for Wasm is progressing at the WasmWG : Module Record Wasm
11. 11 Module Records (Abstract) Module Record Source Text Module Record Cyclic Module Record Synthetic Module Record
12. 12 Module Records (Abstract) Module Record Source Text Module Record Cyclic Module Record Synthetic Module Record Wasm JS JSON, CSS
13. 13 Module Records (Abstract) Module Record Source Text Module Record Cyclic Module Record Synthetic Module Record CommonJS Wasm JS JSON, CSS * no spec
14. 14 Module Records (Abstract) Module Record Source Text Module Record Cyclic Module Record Synthetic Module Record CommonJS Wasm JS JSON, CSS * no spec Due to the spec, the cache cannot be purged (purgeable) cache
15. 15 Import Phase Resolve Load (dependencies) Link Evaluate
16. 16 Import Phase Resolve Load (dependencies) Link Evaluate
17. 17 Import Phase Resolve Load (dependencies) Link Evaluate cache
18. 18 Import Phase Resolve Load (dependencies) Link Evaluate
19. 19 Import Phase Resolve Load (dependencies) Link Evaluate
20. 20 Import Phase Resolve Load (dependencies) Link Evaluate
21. 21 Import Phase Resolve Load (dependencies) Link Evaluate
22. 22 https://speakerdeck.com/uhyo/require -esm-toecmascriptshi-yang
23. Current Proposals 23
26. 26 Module Harmony (2024-12 TC39 meeting)
27. Import Phase Modifiers 27
28. 28 Import Phase Modifiers Resolve Load (dependencies) Link Evaluate modifier: asset source defer import asset ref from "./foo.mjs"; const module = await import.source("./bar.mjs");
29. 29 Asset References Resolve Load (dependencies) Link Evaluate asset source defer import asset ref from "./foo.mjs"; console.log(ref); // AssetReference object const namespace = await import(ref); • No need to change the relative path even when the AssetReference object passes through modules
30. 30 Asset References Resolve Load (dependencies) Link Evaluate asset source defer import asset imageRef from "./foo.png"; const img = new Image(); img.src = URL.createObjectURL(imageRef); • Allows notifying the host (runtime, bundler) about the existence of asset files statically
31. 31 Module Sources Resolve Load (dependencies) Link Evaluate asset source defer (Abstract) Module Source WebAssembly.Module ModuleSource Wasm JS
32. 32 Module Sources Resolve Load (dependencies) Link Evaluate asset source defer import source module from "./foo.wasm"; console.log(module); // WebAssembly.Module object const instance = await WebAssembly.instantiate(module, {/* imports */}); • Wasm modules can be statically added to ES Module Graph • CSP's wasm-unsafe-eval is no longer needed, improving security
33. 33 Module Sources Resolve Load (dependencies) Link Evaluate asset source defer import source module from "./foo.mjs"; console.log(module); // ModuleSource object const worker = new Worker(module); • Modules for Web Workers can be statically added to ES Module Graph • Dynamic Imports work, too
34. 34 Module Sources Resolve Load (dependencies) Link Evaluate asset source defer const workerModule = module { self.addEventListener("message", (e) => {}); }; const worker = new Worker(workerModule); Module Expressions • Possible to create inline modules for Web Workers
35. 35 Deferring Module Eval Resolve Load (dependencies) Link Evaluate asset source defer import defer * as namespace from "./foo.mjs"; namespace.bar; // evaluate "./foo.mjs" • Defer execution until the namespace object's getter is invoked (namespace imports only supported) • Improve initial performance by delaying evaluation
36. 36 Deferring Module Eval Resolve Load (dependencies) Link Evaluate asset source defer // math.mjs export defer { add } from "./math/add.mjs"; export defer { sub } from "./math/sub.mjs"; • Enable "Tree Shaking" without heuristics Deferred re-exports // do not evaluate "./math/sub.mjs" import { add } from "./math.mjs";
37. Other Proposals 37
38. 38 Module Declarations module Foo { export function foo() {} } import { foo } from Foo; • Bundlers' implementation complexity increases with ES Modules ◦ Proposal for additional syntax for bundlers • Optimizing bundled JS files is challenging for engines
39. 39 Import Sync const namespace = import.sync("./foo.mjs"); • Bridge the gap with CommonJS using synchronous dynamic import ◦ Personally, the difference in whether cache can be purged seems like a big gap... • In a browser environment, the main thread cannot be blocked, so it might throw an exception
40. 40 Import Bytes / Text import bytes from "./foo.png" with { type: "bytes" }; // Uint8Array backed by an Immutable ArrayBuffer console.log(bytes); • Add bytes and text support to Synthetic Module Records • Originally proposed in whatwg/html#9444 import text from "./foo.txt" with { type: "text" }; // string (normally) interpreted as UTF-8 console.log(text);
41. To conclude 41
42. My Impressions 42 • ECMAScript has started accepting proposals for non-browser runtimes ◦ It is likely a result of WinterTC's activities ◦ Especially for Module Sources, Deno, Node.js, and Igalia are energetically pushing it forward • Also proposed with consideration for bundlers