feat(core): add Deno.core.loadExtScript() for lazy-loaded scripts#33739
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Adds a new `lazy_loaded_js` parameter to the `extension!` macro and a `Deno.core.loadExtScript(specifier)` API that loads and evaluates scripts on demand. This is an alternative to `lazy_loaded_esm` / `createLazyLoader()` that avoids V8's ES module infrastructure entirely. Scripts loaded this way don't create module records, namespace objects, or module graph edges, resulting in smaller snapshots and faster serialization/deserialization. Scripts are expected to be wrapped in an IIFE and use `return` to provide exports. They access `core` and `primordials` via `globalThis.__bootstrap`. Results are cached on the JS side so each script is evaluated at most once. Circular dependencies are detected and cause an error. As a proof of concept, `ext/webstorage/01_webstorage.js` is migrated from ESM (`esm = [...]`) to lazy script (`lazy_loaded_js = [...]`).
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Converts `ext/webidl/00_webidl.js` from ESM (`esm = [...]`) to a
lazy-loaded script (`lazy_loaded_js = [...]`). This removes 1 module
record, 1 namespace object, and all associated module graph edges from
the V8 snapshot.
All 36 consumer files across ext/web, ext/fetch, ext/cache, ext/crypto,
ext/websocket, ext/webgpu, ext/image, ext/node, and runtime/ are updated
to use `core.loadExtScript("ext:deno_webidl/00_webidl.js")` instead of
`import * as webidl from "ext:deno_webidl/00_webidl.js"`. Files that
only imported `primordials` from `ext:core/mod.js` now also import
`core`.
Converts three more ext/web files from ESM to lazy-loaded scripts: - `02_timers.js` - setTimeout/setInterval (2 consumers updated) - `01_dom_exception.js` - DOMException class (18 consumers updated) Uses lazy loading for console's createFilteredInspectProxy to avoid circular dependency with the still-ESM console module. - `05_base64.js` - atob/btoa (2 consumers updated) All consumer files across ext/ and runtime/ are updated to use `core.loadExtScript()` instead of ESM imports.
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…33760) - Converts all 24 ext/web JS files from ESM modules to IIFE-wrapped lazy-loaded scripts using `core.loadExtScript()`, building on the infrastructure from #33739 - Updates all external consumers across `ext/`, `runtime/`, and `cli/` from `import` to `core.loadExtScript()` - Replaces `createLazyLoader()` calls targeting ext:deno_web files with `loadExtScript()` since they are now plain scripts ## Notes - `import.meta.log` in `06_streams.js` replaced with `core.print()` as a temporary workaround since `import.meta` is not available in non-module scripts. A proper `core.log` equivalent may be needed.
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Summary
Adds
Deno.core.loadExtScript(specifier)— a new API for loading extensionscripts on demand without going through V8's ES module infrastructure.
Motivation: Benchmarking showed that ES modules add ~31% snapshot size
overhead and ~4x slower serialization/deserialization compared to plain scripts
(investigation gist).
For extensions that don't need
import/exportsemantics, using scriptsinstead of ESM can significantly reduce snapshot size and improve startup time.
What's included:
lazy_loaded_jsparameter in theextension!macro (analogous tolazy_loaded_esm)op_load_ext_scriptop that evaluates a script and returns the resultDeno.core.loadExtScript(specifier)JS API with JS-side result cachingext/webstorage/01_webstorage.jsfrom ESM to lazy scriptScript convention: Files are manually wrapped in an IIFE, access core via
globalThis.__bootstrap, and usereturnfor exports. Oncedenoland/rusty_v8#1973 lands,
we can switch to automatic IIFE wrapping via
v8::String::Concatto avoidneeding to reformat files.
Test plan
cargo test -p deno_core test_lazy_loaded_script— unit tests passcargo build --bin deno— full binary builds with snapshotdeno eval 'localStorage.setItem("k","v"); console.log(localStorage.getItem("k"))'works