feat: Support returning values from scripts executed with the scripting API

src/types/index.ts

@@ -737,16 +737,24 @@ export interface IsolatedWorldContentScriptDefinition
   extends IsolatedWorldContentScriptEntrypointOptions {
   /**
    * Main function executed when the content script is loaded.
+   *
+   * When running a content script with `browser.scripting.executeScript`,
+   * values returned from this function will be returned in the `executeScript`
+   * result as well. Otherwise returning a value does nothing.
    */
-  main(ctx: ContentScriptContext): void | Promise<void>;
+  main(ctx: ContentScriptContext): any | Promise<any>;
 }
 
 export interface MainWorldContentScriptDefinition
   extends MainWorldContentScriptEntrypointOptions {
   /**
    * Main function executed when the content script is loaded.
+   *
+   * When running a content script with `browser.scripting.executeScript`,
+   * values returned from this function will be returned in the `executeScript`
+   * result as well. Otherwise returning a value does nothing.
    */
-  main(): void | Promise<void>;
+  main(): any | Promise<any>;
 }
 
 export type ContentScriptDefinition =
@@ -763,8 +771,12 @@ export interface BackgroundDefinition extends BackgroundEntrypointOptions {
 export interface UnlistedScriptDefinition extends BaseEntrypointOptions {
   /**
    * Main function executed when the unlisted script is ran.
+   *
+   * When running a content script with `browser.scripting.executeScript`,
+   * values returned from this function will be returned in the `executeScript`
+   * result as well. Otherwise returning a value does nothing.
    */
-  main(): void | Promise<void>;
+  main(): any | Promise<any>;
 }
 
 /**

src/virtual/content-script-isolated-world-entrypoint.ts

@@ -2,16 +2,22 @@ import definition from 'virtual:user-content-script-isolated-world-entrypoint';
 import { logger } from '../sandbox/utils/logger';
 import { ContentScriptContext } from 'wxt/client';
 
-(async () => {
+const result = (async () => {
   try {
     const { main, ...options } = definition;
     const ctx = new ContentScriptContext(import.meta.env.ENTRYPOINT, options);
 
-    await main(ctx);
+    return await main(ctx);
   } catch (err) {
     logger.error(
       `The content script "${import.meta.env.ENTRYPOINT}" crashed on startup!`,
       err,
     );
+    throw err;
   }
 })();
+
+// Return the main function's result to the background when executed via the scripting API.
+// https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/scripting/executeScript#return_value
+// Tested on both Chrome and Firefox
+result;

src/virtual/content-script-main-world-entrypoint.ts

@@ -1,14 +1,20 @@
 import definition from 'virtual:user-content-script-main-world-entrypoint';
 import { logger } from '../sandbox/utils/logger';
 
-(async () => {
+const result = (async () => {
   try {
     const { main } = definition;
-    await main();
+    return await main();
   } catch (err) {
     logger.error(
       `The content script "${import.meta.env.ENTRYPOINT}" crashed on startup!`,
       err,
     );
+    throw err;
   }
 })();
+
+// Return the main function's result to the background when executed via the scripting API.
+// https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/scripting/executeScript#return_value
+// Tested on both Chrome and Firefox
+result;

src/virtual/unlisted-script-entrypoint.ts

@@ -1,13 +1,19 @@
 import definition from 'virtual:user-unlisted-script-entrypoint';
 import { logger } from '../sandbox/utils/logger';
 
-(async () => {
+const result = (async () => {
   try {
-    await definition.main();
+    return await definition.main();
   } catch (err) {
     logger.error(
       `The unlisted script "${import.meta.env.ENTRYPOINT}" crashed on startup!`,
       err,
     );
+    throw err;
   }
 })();
+
+// Return the main function's result to the background when executed via the scripting API.
+// https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/scripting/executeScript#return_value
+// Tested on both Chrome and Firefox
+result;