Add dynamic module loader to flutter wasm entrypoint script. (#169313)

biggs0125 · natebiggs · web-flow · commit f5f9f351f0f8 · 2025-05-28T21:47:17.000Z
Adds support for loading dynamic module files to the Flutter wasm entrypoint script. The Dart SDK already tries to import this function when dynamic modules are enabled. ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [x] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant documentation (doc comments with `///`). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [ ] All existing and new tests are passing. If you need help, consider asking for advice on the #hackers-new channel on [Discord].  [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md --------- Co-authored-by: Nate Biggs <natebiggs@google.com>
diff --git a/engine/src/flutter/lib/web_ui/flutter_js/src/entrypoint_loader.js b/engine/src/flutter/lib/web_ui/flutter_js/src/entrypoint_loader.js
@@ -174,7 +174,17 @@ export class FlutterEntrypointLoader {
         importsPromise = Promise.resolve({});
       }
       const compiledDartApp = await compiledDartAppPromise;
-      const dartApp = await compiledDartApp.instantiate(await importsPromise);
+      const dartApp = await compiledDartApp.instantiate(await importsPromise, {
+        loadDynamicModule: async (wasmUri, mjsUri) => {
+          const wasmBytes = fetch(resolveUrlWithSegments(entrypointBaseUrl, wasmUri));
+          let mjsRuntimeUri = resolveUrlWithSegments(entrypointBaseUrl, mjsUri);
+          if (this._ttPolicy != null) {
+            mjsRuntimeUri = this._ttPolicy.createScriptURL(mjsRuntimeUri);
+          }
+          const mjsModule = import(mjsRuntimeUri);
+          return [await wasmBytes, await mjsModule];
+        }
+      });
       await dartApp.invokeMain();
     }
   }

Original file line number	Diff line number	Diff line change
`@@ -174,7 +174,17 @@ export class FlutterEntrypointLoader {`
`174`	`174`	`importsPromise = Promise.resolve({});`
`175`	`175`	`}`
`176`	`176`	`const compiledDartApp = await compiledDartAppPromise;`
`177`		`- const dartApp = await compiledDartApp.instantiate(await importsPromise);`
	`177`	`+ const dartApp = await compiledDartApp.instantiate(await importsPromise, {`
	`178`	`+ loadDynamicModule: async (wasmUri, mjsUri) => {`
	`179`	`+ const wasmBytes = fetch(resolveUrlWithSegments(entrypointBaseUrl, wasmUri));`
	`180`	`+ let mjsRuntimeUri = resolveUrlWithSegments(entrypointBaseUrl, mjsUri);`
	`181`	`+ if (this._ttPolicy != null) {`
	`182`	`+ mjsRuntimeUri = this._ttPolicy.createScriptURL(mjsRuntimeUri);`
	`183`	`+ }`
	`184`	`+ const mjsModule = import(mjsRuntimeUri);`
	`185`	`+ return [await wasmBytes, await mjsModule];`
	`186`	`+ }`
	`187`	`+ });`
`178`	`188`	`await dartApp.invokeMain();`
`179`	`189`	`}`
`180`	`190`	`}`