feat: add initSync() to initialize WASM synchronously (#100)

This uses the synchronous WebAssembly APIs to compile the WASM
part synchronously, which allows users to initialize the library
and parse synchronously with WASM without having to resort
to the JS version. This would be useful for Node.js core to
use the WASM version in paths that require synchronous
initialization (it currently always uses the JS version for that).

Author: joyeecheung

README.md

@@ -59,7 +59,8 @@ When using the ESM version, Wasm is supported instead:
 
 ```js
 import { parse, init } from 'cjs-module-lexer';
-// init needs to be called and waited upon
+// init() needs to be called and waited upon, or use initSync() to compile
+// Wasm blockingly and synchronously.
 await init();
 const { exports, reexports } = parse(source);
 ```

lexer.d.ts

@@ -5,3 +5,4 @@ export interface Exports {
 
 export declare function parse(source: string, name?: string): Exports;
 export declare function init(): Promise<void>;
+export declare function initSync(): void;

lexer.js

@@ -1439,4 +1439,5 @@ function isExpressionTerminator (curPos) {
 const initPromise = Promise.resolve();
 
 module.exports.init = () => initPromise;
+module.exports.initSync = () => {};
 module.exports.parse = parseCJS;

package.json

@@ -14,7 +14,8 @@
   "scripts": {
     "test-js": "mocha -b -u tdd test/*.js",
     "test-wasm": "cross-env WASM=1 mocha -b -u tdd test/*.js",
-    "test": "npm run test-wasm && npm run test-js",
+    "test-wasm-sync": "cross-env WASM_SYNC=1 mocha -b -u tdd test/*.js",
+    "test": "npm run test-wasm && npm run test-wasm-sync && npm run test-js",
     "bench": "node --expose-gc bench/index.mjs",
     "build": "node build.js ; babel dist/lexer.mjs -o dist/lexer.js ; terser dist/lexer.js -o dist/lexer.js",
     "build-wasm": "make lib/lexer.wasm && node build.js",

src/lexer.js

@@ -90,16 +90,30 @@ function copyLE (src, outBuf16) {
     outBuf16[i] = src.charCodeAt(i++);
 }
 
+function getWasmBytes() {
+  const binary = 'WASM_BINARY';  // This string will be replaced by build.js.
+  if (typeof window !== 'undefined' && typeof atob === 'function')
+    return Uint8Array.from(atob(binary), x => x.charCodeAt(0));
+  return Buffer.from(binary, 'base64');
+}
+
 let initPromise;
 export function init () {
   if (initPromise)
     return initPromise;
   return initPromise = (async () => {
-    const compiled = await WebAssembly.compile(
-      (binary => typeof window !== 'undefined' && typeof atob === 'function' ? Uint8Array.from(atob(binary), x => x.charCodeAt(0)) : Buffer.from(binary, 'base64'))
-      ('WASM_BINARY')
-    )
+    const compiled = await WebAssembly.compile(getWasmBytes());
     const { exports } = await WebAssembly.instantiate(compiled);
     wasm = exports;
   })();
 }
+
+export function initSync () {
+  if (wasm) {
+    return;
+  }
+  const compiled = new WebAssembly.Module(getWasmBytes());
+  const { exports } = new WebAssembly.Instance(compiled);
+  wasm = exports;
+  return;
+}

test/_unit.js

@@ -7,6 +7,10 @@ async function loadParser () {
     const m = await import('../dist/lexer.mjs');
     await m.init();
     parse = m.parse;
+  } else if (process.env.WASM_SYNC) {
+    const m = require('../dist/lexer.js');
+    m.initSync();
+    parse = m.parse;
   }
   else {
     parse = require('../lexer.js').parse;

test/integration.js

@@ -8,6 +8,10 @@ async function loadParser () {
     const m = await import('../dist/lexer.mjs');
     await m.init();
     parse = m.parse;
+  } else if (process.env.WASM_SYNC) {
+    const m = require('../dist/lexer.js');
+    m.initSync();
+    parse = m.parse;
   }
   else {
     parse = require('../lexer.js').parse;
@@ -31,7 +35,7 @@ suite('Samples', () => {
   const selfSource = fs.readFileSync(process.cwd() + '/lexer.js').toString();
   test('Self test', async () => {
     const { exports } = parse(selfSource);
-    assert.deepStrictEqual(exports, ['init', 'parse']);
+    assert.deepStrictEqual(exports, ['init', 'initSync', 'parse']);
   });
 
   files.forEach(({ file, code }) => {