feat: improve JavaScript performance by caching the runtime + polyfill (

#257)

* feat: improve JS runtime performance by caching polyfill with wizer

* feat: update JS engine with the latest compilation

kits/javascript/Cargo.toml

@@ -11,3 +11,4 @@ javy = { version = "2.0.0", features = ["json"] }
 regex = "1.10.1"
 # Use an old version until we add support for components.
 wit-bindgen-rust = { git = "https://github.com/bytecodealliance/wit-bindgen", rev = "cb871cfa1ee460b51eb1d144b175b9aab9c50aba" }
+once_cell = "1.18.0"

kits/javascript/Makefile

@@ -1,5 +1,7 @@
-.PHONY: build
+.PHONY: build build-src
 
-build:
-	cargo build --target wasm32-wasi --release && \
-	cp ./target/wasm32-wasi/release/wasm-workers-quick-js-engine.wasm ./
+build-src:
+	cargo build --target wasm32-wasi --release
+
+build: build-src
+	wizer --allow-wasi --wasm-bulk-memory true -o ./wasm-workers-quick-js-engine.wasm ./target/wasm32-wasi/release/wasm-workers-quick-js-engine.wasm

kits/javascript/src/error.rs

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 /// List of runtime errors
+#[derive(Debug)]
 pub enum RuntimeError {
     InvalidBinding { invalid_export: String },
 }

kits/javascript/src/main.rs

@@ -6,6 +6,7 @@ mod error;
 
 use bindings::load_bindings_into_global;
 use javy::{json, Runtime};
+use once_cell::sync::OnceCell;
 use regex::Regex;
 use std::{
     env, fs,
@@ -15,9 +16,28 @@ use std::{
 // Load bindings from WIT file.
 wit_bindgen_rust::import!({paths: ["../../wit/core/http.wit"]});
 
+/// Ready to use runtime + polyfill
+static mut RUNTIME: OnceCell<Runtime> = OnceCell::new();
+
 // JS polyfill
 static POLYFILL: &str = include_str!("../shims/dist/index.js");
 
+/// Preinitialize the module with Wizer
+#[export_name = "wizer.initialize"]
+pub extern "C" fn init() {
+    let runtime = Runtime::default();
+
+    // Precompile the Polyfill to bytecode
+    let context = runtime.context();
+    let bytecode = context.compile_global("polyfill.js", POLYFILL).unwrap();
+
+    // Preload it
+    let _ = context.eval_binary(&bytecode);
+
+    // Store result
+    unsafe { RUNTIME.set(runtime).unwrap() };
+}
+
 /// Determine the worker JS type
 enum JSWorkerType {
     /// Relies on the global scope. No ECMA modules.
@@ -47,13 +67,12 @@ fn identify_type(src: &str) -> JSWorkerType {
 }
 
 fn main() {
-    let runtime = Runtime::default();
+    let runtime = unsafe { RUNTIME.get().unwrap() };
     let context = runtime.context();
 
     let source = fs::read_to_string("/src/index.js");
     let mut contents = String::new();
     let mut request = String::new();
-    contents.push_str(POLYFILL);
 
     stdin().read_to_string(&mut request).unwrap();