Correctly set worker's output format if not support by environment

packages/core/core/src/requests/TargetRequest.js

@@ -225,7 +225,9 @@ export class TargetResolver {
                 context: descriptor.context,
                 isLibrary: descriptor.isLibrary,
                 includeNodeModules: descriptor.includeNodeModules,
-                outputFormat: descriptor.outputFormat,
+                outputFormat:
+                  descriptor.outputFormat ??
+                  this.options.defaultTargetOptions.outputFormat,
                 shouldOptimize:
                   this.options.defaultTargetOptions.shouldOptimize &&
                   descriptor.optimize !== false,
@@ -291,6 +293,7 @@ export class TargetResolver {
               context: 'browser',
               engines: {},
               shouldOptimize: this.options.defaultTargetOptions.shouldOptimize,
+              outputFormat: this.options.defaultTargetOptions.outputFormat,
               shouldScopeHoist: this.options.defaultTargetOptions
                 .shouldScopeHoist,
               sourceMap: this.options.defaultTargetOptions.sourceMaps
@@ -590,6 +593,7 @@ export class TargetResolver {
 
         let outputFormat =
           descriptor.outputFormat ??
+          this.options.defaultTargetOptions.outputFormat ??
           inferredOutputFormat ??
           (targetName === 'module' ? 'esmodule' : 'commonjs');
         let isModule = outputFormat === 'esmodule';
@@ -753,7 +757,10 @@ export class TargetResolver {
             context: descriptor.context,
             includeNodeModules: descriptor.includeNodeModules,
             outputFormat:
-              descriptor.outputFormat ?? inferredOutputFormat ?? undefined,
+              descriptor.outputFormat ??
+              this.options.defaultTargetOptions.outputFormat ??
+              inferredOutputFormat ??
+              undefined,
             isLibrary: descriptor.isLibrary,
             shouldOptimize:
               this.options.defaultTargetOptions.shouldOptimize &&
@@ -779,6 +786,7 @@ export class TargetResolver {
         env: createEnvironment({
           engines: pkgEngines,
           context,
+          outputFormat: this.options.defaultTargetOptions.outputFormat,
           shouldOptimize: this.options.defaultTargetOptions.shouldOptimize,
           shouldScopeHoist: this.options.defaultTargetOptions.shouldScopeHoist,
           sourceMap: this.options.defaultTargetOptions.sourceMaps

packages/core/core/src/resolveOptions.js

@@ -148,6 +148,7 @@ export default async function resolveOptions(
       publicUrl,
       distDir,
       engines: initialOptions?.defaultTargetOptions?.engines,
+      outputFormat: initialOptions?.defaultTargetOptions?.outputFormat,
     },
   };
 }

packages/core/core/src/types.js

@@ -235,6 +235,7 @@ export type ParcelOptions = {|
     +publicUrl: string,
     +distDir?: FilePath,
     +engines?: Engines,
+    +outputFormat?: OutputFormat,
   |},
 |};
 

packages/core/integration-tests/test/javascript.js

@@ -851,15 +851,17 @@ describe('javascript', function() {
     assert(/new SharedWorker(.*?, {[\n\s]+type: 'module'[\n\s]+})/.test(main));
   });
 
-  for (let scopeHoist of [true, false]) {
+  for (let shouldScopeHoist of [true, false]) {
     it(`should compile workers to non modules if ${
-      scopeHoist ? 'browsers do not support it' : 'scopeHoist = false'
+      shouldScopeHoist
+        ? 'browsers do not support it'
+        : 'shouldScopeHoist = false'
     }`, async function() {
       let b = await bundle(
         path.join(__dirname, '/integration/workers-module/index.js'),
         {
           defaultTargetOptions: {
-            shouldScopeHoist: true,
+            shouldScopeHoist,
             engines: {
               browsers: '>= 0.25%',
             },
@@ -869,14 +871,22 @@ describe('javascript', function() {
 
       assertBundles(b, [
         {
-          assets: ['dedicated-worker.js', 'index.js'],
+          assets: [
+            'dedicated-worker.js',
+            !shouldScopeHoist && 'esmodule-helpers.js',
+            'index.js',
+          ].filter(Boolean),
         },
         {
           name: 'index.js',
           assets: ['index.js', 'bundle-url.js', 'get-worker-url.js'],
         },
         {
-          assets: ['shared-worker.js', 'index.js'],
+          assets: [
+            !shouldScopeHoist && 'esmodule-helpers.js',
+            'shared-worker.js',
+            'index.js',
+          ].filter(Boolean),
         },
       ]);
 
@@ -905,6 +915,71 @@ describe('javascript', function() {
     });
   }
 
+  for (let supported of [false, true]) {
+    it(`should compile workers to ${
+      supported ? '' : 'non '
+    }modules when browsers do ${
+      supported ? '' : 'not '
+    }support it with esmodule parent script`, async function() {
+      let b = await bundle(
+        path.join(__dirname, '/integration/workers-module/index.js'),
+        {
+          mode: 'production',
+          defaultTargetOptions: {
+            engines: {browsers: supported ? 'Chrome 80' : 'Chrome 75'},
+            outputFormat: 'esmodule',
+            shouldScopeHoist: true,
+            shouldOptimize: false,
+          },
+        },
+      );
+
+      assertBundles(b, [
+        {
+          type: 'js',
+          assets: ['dedicated-worker.js'],
+        },
+        {
+          name: 'index.js',
+          assets: ['index.js', 'bundle-url.js', 'get-worker-url.js'],
+        },
+        {
+          type: 'js',
+          assets: ['shared-worker.js'],
+        },
+        {
+          type: 'js',
+          assets: ['index.js'],
+        },
+      ]);
+
+      let dedicated, shared;
+      b.traverseBundles((bundle, ctx, traversal) => {
+        if (bundle.getMainEntry()?.filePath.endsWith('shared-worker.js')) {
+          shared = bundle;
+        } else if (
+          bundle.getMainEntry()?.filePath.endsWith('dedicated-worker.js')
+        ) {
+          dedicated = bundle;
+        }
+        if (dedicated && shared) traversal.stop();
+      });
+
+      assert(dedicated);
+      assert(shared);
+
+      let main = await outputFS.readFile(b.getBundles()[0].filePath, 'utf8');
+      assert(/new Worker([^,]*?)/.test(main));
+      assert(/new SharedWorker([^,]*?)/.test(main));
+
+      dedicated = await outputFS.readFile(dedicated.filePath, 'utf8');
+      shared = await outputFS.readFile(shared.filePath, 'utf8');
+      let importRegex = supported ? /importScripts\s*\(/ : /import\s*("|')/;
+      assert(!importRegex.test(dedicated));
+      assert(!importRegex.test(shared));
+    });
+  }
+
   it('should preserve the name option to workers', async function() {
     let b = await bundle(
       path.join(__dirname, '/integration/workers-module/named.js'),

packages/core/types/index.js

@@ -309,6 +309,7 @@ export type InitialParcelOptions = {|
     +publicUrl?: string,
     +distDir?: FilePath,
     +engines?: Engines,
+    +outputFormat?: OutputFormat,
   |},
 
   +additionalReporters?: Array<{|

packages/transformers/js/src/JSTransformer.js

@@ -484,15 +484,18 @@ export default (new Transformer({
     for (let dep of dependencies) {
       if (dep.kind === 'WebWorker') {
         // Use native ES module output if the worker was created with `type: 'module'` and all targets
-        // support native module workers. Only do this if the source type is changing from script to module
-        // though so that assets can be shared between workers and the main thread in the global output format.
-        let outputFormat = asset.env.outputFormat;
+        // support native module workers. Only do this if parent asset output format is also esmodule so that
+        // assets can be shared between workers and the main thread in the global output format.
+        let outputFormat;
         if (
-          asset.env.sourceType === 'script' &&
+          asset.env.outputFormat === 'esmodule' &&
           dep.source_type === 'Module' &&
           supportsModuleWorkers
         ) {
           outputFormat = 'esmodule';
+        } else {
+          outputFormat =
+            asset.env.outputFormat === 'commonjs' ? 'commonjs' : 'global';
         }
 
         let loc = convertLoc(dep.loc);