From 9d3079a21ed318023f48fc0ae39444c85204d029 Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Wed, 15 Dec 2021 18:55:20 +0800
Subject: [PATCH 01/12] Add support for customizing worker options

---
 packages/vite/src/node/plugins/worker.ts | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/packages/vite/src/node/plugins/worker.ts b/packages/vite/src/node/plugins/worker.ts
index 799233088d6b13..e34b7634680ea4 100644
--- a/packages/vite/src/node/plugins/worker.ts
+++ b/packages/vite/src/node/plugins/worker.ts
@@ -77,10 +77,13 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
           // inline as blob data url
           return `const encodedJs = "${content.toString('base64')}";
             const blob = typeof window !== "undefined" && window.Blob && new Blob([atob(encodedJs)], { type: "text/javascript;charset=utf-8" });
-            export default function WorkerWrapper() {
+            export default function WorkerWrapper(workerOptions) {
               const objURL = blob && (window.URL || window.webkitURL).createObjectURL(blob);
               try {
-                return objURL ? new Worker(objURL) : new Worker("data:application/javascript;base64," + encodedJs, {type: "module"});
+                return objURL ? new Worker(objURL) : new Worker(
+                  "data:application/javascript;base64," + encodedJs,
+                  Object.assign({ type: "module" }, workerOptions)
+                );
               } finally {
                 objURL && (window.URL || window.webkitURL).revokeObjectURL(objURL);
               }
@@ -105,12 +108,12 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
 
       const workerConstructor =
         query.sharedworker != null ? 'SharedWorker' : 'Worker'
-      const workerOptions = { type: 'module' }
 
-      return `export default function WorkerWrapper() {
-        return new ${workerConstructor}(${JSON.stringify(
-        url
-      )}, ${JSON.stringify(workerOptions, null, 2)})
+      return `export default function WorkerWrapper(workerOptions) {
+        return new ${workerConstructor}(
+          ${JSON.stringify(url)},
+          Object.assign({ type: "module" }, workerOptions)
+        )
       }`
     }
   }

From 68363059400e9cc029de2088108b42aa27123b9f Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Thu, 16 Dec 2021 00:14:21 +0800
Subject: [PATCH 02/12] Handle env in classic worker (wip)

---
 packages/vite/src/node/plugins/worker.ts | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/packages/vite/src/node/plugins/worker.ts b/packages/vite/src/node/plugins/worker.ts
index e34b7634680ea4..ff039e29881aef 100644
--- a/packages/vite/src/node/plugins/worker.ts
+++ b/packages/vite/src/node/plugins/worker.ts
@@ -1,3 +1,5 @@
+
+import fs from 'fs'
 import { ResolvedConfig } from '../config'
 import { Plugin } from '../plugin'
 import { resolvePlugins } from '../plugins'
@@ -5,10 +7,17 @@ import { parse as parseUrl, URLSearchParams } from 'url'
 import { fileToUrl, getAssetHash } from './asset'
 import { cleanUrl, injectQuery } from '../utils'
 import Rollup from 'rollup'
-import { ENV_PUBLIC_PATH } from '../constants'
+import { ENV_PUBLIC_PATH, ENV_ENTRY } from '../constants'
 import path from 'path'
 import { onRollupWarning } from '../build'
 
+function loadEnvScript(): string {
+  const script = fs.readFileSync(ENV_ENTRY, 'utf-8');
+  return script.replace(/\n\/\/# sourceMappingURL=.*\n/, '\n');
+}
+
+console.log(loadEnvScript())
+
 function parseWorkerRequest(id: string): Record<string, string> | null {
   const { search } = parseUrl(id)
   if (!search) {
@@ -80,8 +89,8 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
             export default function WorkerWrapper(workerOptions) {
               const objURL = blob && (window.URL || window.webkitURL).createObjectURL(blob);
               try {
-                return objURL ? new Worker(objURL) : new Worker(
-                  "data:application/javascript;base64," + encodedJs,
+                return new Worker(
+                  objURL || ("data:application/javascript;base64," + encodedJs),
                   Object.assign({ type: "module" }, workerOptions)
                 );
               } finally {

From aaa26c6adeec3fef28cea9c2c3eb20009f32b78e Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Thu, 16 Dec 2021 00:14:41 +0800
Subject: [PATCH 03/12] Add tests

---
 packages/playground/worker/__tests__/worker.spec.ts |  5 +++++
 packages/playground/worker/classic-worker.ts        |  5 +++++
 packages/playground/worker/index.html               | 13 +++++++++++++
 3 files changed, 23 insertions(+)
 create mode 100644 packages/playground/worker/classic-worker.ts

diff --git a/packages/playground/worker/__tests__/worker.spec.ts b/packages/playground/worker/__tests__/worker.spec.ts
index 46b136edd66d2a..1fde16117a033e 100644
--- a/packages/playground/worker/__tests__/worker.spec.ts
+++ b/packages/playground/worker/__tests__/worker.spec.ts
@@ -22,6 +22,11 @@ test('inlined', async () => {
   await untilUpdated(() => page.textContent('.pong-inline'), 'pong')
 })
 
+test('worker options', async () => {
+  await page.click('.ping-classic')
+  await untilUpdated(() => page.textContent('.pong-classic'), 'pong')
+})
+
 const waitSharedWorkerTick = (
   (resolvedSharedWorkerCount: number) => async (page: Page) => {
     await untilUpdated(async () => {
diff --git a/packages/playground/worker/classic-worker.ts b/packages/playground/worker/classic-worker.ts
new file mode 100644
index 00000000000000..7f7e55b1a9c542
--- /dev/null
+++ b/packages/playground/worker/classic-worker.ts
@@ -0,0 +1,5 @@
+self.onmessage = (e) => {
+  if (e.data === 'ping') {
+    self.postMessage('pong')
+  }
+}
diff --git a/packages/playground/worker/index.html b/packages/playground/worker/index.html
index 1ce429eece42cc..c652e382308c2f 100644
--- a/packages/playground/worker/index.html
+++ b/packages/playground/worker/index.html
@@ -7,6 +7,9 @@
 <button class="ping-inline">Ping Inline Worker</button>
 <div>Response from inline worker: <span class="pong-inline"></span></div>
 
+<button class="ping-classic">Ping Classic Worker</button>
+<div>Response from classic worker: <span class="pong-classic"></span></div>
+
 <button class="ping-ts-output">Ping Possible Compiled TS Worker</button>
 <div>
   Response from worker imported from code that might be compiled TS:
@@ -22,6 +25,7 @@
 <script type="module">
   import Worker from './my-worker?worker'
   import InlineWorker from './my-worker?worker&inline'
+  import ClassicWorker from './classic-worker?worker'
   import SharedWorker from './my-shared-worker?sharedworker&name=shared'
   import TSOutputWorker from './possible-ts-output-worker?worker'
   import { mode } from './workerImport'
@@ -47,6 +51,15 @@
     inlineWorker.postMessage('ping')
   })
 
+  const classicWorker = new ClassicWorker({ type: 'classic' })
+  classicWorker.addEventListener('message', (e) => {
+    text('.pong-classic', e.data)
+  })
+
+  document.querySelector('.ping-classic').addEventListener('click', () => {
+    classicWorker.postMessage('ping')
+  })
+
   const sharedWorker = new SharedWorker()
   document.querySelector('.tick-shared').addEventListener('click', () => {
     sharedWorker.port.postMessage('tick')

From 68b311a262af6b0d0cdc83c73184a14b382f5e1b Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Thu, 16 Dec 2021 01:37:51 +0800
Subject: [PATCH 04/12] Inject env into classic workers with
 `self.importScripts`

---
 packages/vite/src/node/plugins/worker.ts | 58 ++++++++++++++----------
 1 file changed, 33 insertions(+), 25 deletions(-)

diff --git a/packages/vite/src/node/plugins/worker.ts b/packages/vite/src/node/plugins/worker.ts
index ff039e29881aef..dc7526d155a02d 100644
--- a/packages/vite/src/node/plugins/worker.ts
+++ b/packages/vite/src/node/plugins/worker.ts
@@ -1,5 +1,4 @@
 
-import fs from 'fs'
 import { ResolvedConfig } from '../config'
 import { Plugin } from '../plugin'
 import { resolvePlugins } from '../plugins'
@@ -7,17 +6,10 @@ import { parse as parseUrl, URLSearchParams } from 'url'
 import { fileToUrl, getAssetHash } from './asset'
 import { cleanUrl, injectQuery } from '../utils'
 import Rollup from 'rollup'
-import { ENV_PUBLIC_PATH, ENV_ENTRY } from '../constants'
+import { ENV_PUBLIC_PATH } from '../constants'
 import path from 'path'
 import { onRollupWarning } from '../build'
 
-function loadEnvScript(): string {
-  const script = fs.readFileSync(ENV_ENTRY, 'utf-8');
-  return script.replace(/\n\/\/# sourceMappingURL=.*\n/, '\n');
-}
-
-console.log(loadEnvScript())
-
 function parseWorkerRequest(id: string): Record<string, string> | null {
   const { search } = parseUrl(id)
   if (!search) {
@@ -27,6 +19,7 @@ function parseWorkerRequest(id: string): Record<string, string> | null {
 }
 
 const WorkerFileId = 'worker_file'
+const ClassicWorkerQuery = 'classic'
 
 export function webWorkerPlugin(config: ResolvedConfig): Plugin {
   const isBuild = config.command === 'build'
@@ -49,8 +42,14 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
     async transform(_, id) {
       const query = parseWorkerRequest(id)
       if (query && query[WorkerFileId] != null) {
-        return {
-          code: `import '${ENV_PUBLIC_PATH}'\n` + _
+        if (query[ClassicWorkerQuery] != null) {
+          return {
+            code: `self.importScripts(${JSON.stringify(ENV_PUBLIC_PATH)})\n` + _
+          }
+        } else {
+          return {
+            code: `import '${ENV_PUBLIC_PATH}'\n` + _
+          }
         }
       }
       if (
@@ -60,7 +59,9 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
         return
       }
 
-      let url: string
+      const workerConstructor =
+        query.sharedworker != null ? 'SharedWorker' : 'Worker'
+
       if (isBuild) {
         // bundle the file as entry to support imports
         const rollup = require('rollup') as typeof Rollup
@@ -97,33 +98,40 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
                 objURL && (window.URL || window.webkitURL).revokeObjectURL(objURL);
               }
             }`
-        } else {
+        } else { // isBuild: true, inline: false
           const basename = path.parse(cleanUrl(id)).name
           const contentHash = getAssetHash(content)
           const fileName = path.posix.join(
             config.build.assetsDir,
             `${basename}.${contentHash}.js`
           )
-          url = `__VITE_ASSET__${this.emitFile({
+          const url = `__VITE_ASSET__${this.emitFile({
             fileName,
             type: 'asset',
             source: code
           })}__`
+
+          return `export default function WorkerWrapper(workerOptions) {
+            return new ${workerConstructor}(
+              ${JSON.stringify(url)},
+              Object.assign({ type: "module" }, workerOptions)
+            )
+          }`
         }
-      } else {
-        url = await fileToUrl(cleanUrl(id), config, this)
+      } else { // isBuild: false
+        let url = await fileToUrl(cleanUrl(id), config, this)
         url = injectQuery(url, WorkerFileId)
-      }
 
-      const workerConstructor =
-        query.sharedworker != null ? 'SharedWorker' : 'Worker'
+        return `export default function WorkerWrapper(workerOptions) {
+          workerOptions = Object.assign({ type: "module" }, workerOptions)
+          let url = ${JSON.stringify(url)}
+          if (workerOptions.type !== "module") {
+            url += ${JSON.stringify('&' + ClassicWorkerQuery)}
+          }
+          return new ${workerConstructor}(url, workerOptions)
+        }`
+      }
 
-      return `export default function WorkerWrapper(workerOptions) {
-        return new ${workerConstructor}(
-          ${JSON.stringify(url)},
-          Object.assign({ type: "module" }, workerOptions)
-        )
-      }`
     }
   }
 }

From 92a9c96fff0ec721e630a993d2dff36f2b84c48d Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Thu, 16 Dec 2021 22:07:42 +0800
Subject: [PATCH 05/12] Update d.ts for workerOptions parameter

---
 packages/vite/client.d.ts                | 2 +-
 packages/vite/src/node/plugins/worker.ts | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/vite/client.d.ts b/packages/vite/client.d.ts
index 2586f07816cade..a9fc19ebe9dfcc 100644
--- a/packages/vite/client.d.ts
+++ b/packages/vite/client.d.ts
@@ -169,7 +169,7 @@ declare module '*.pdf' {
 // web worker
 declare module '*?worker' {
   const workerConstructor: {
-    new (): Worker
+    new (workerOptions?: WorkerOptions): Worker
   }
   export default workerConstructor
 }
diff --git a/packages/vite/src/node/plugins/worker.ts b/packages/vite/src/node/plugins/worker.ts
index dc7526d155a02d..a98c216d613a3c 100644
--- a/packages/vite/src/node/plugins/worker.ts
+++ b/packages/vite/src/node/plugins/worker.ts
@@ -44,7 +44,7 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
       if (query && query[WorkerFileId] != null) {
         if (query[ClassicWorkerQuery] != null) {
           return {
-            code: `self.importScripts(${JSON.stringify(ENV_PUBLIC_PATH)})\n` + _
+            code: `self.importScripts(${JSON.stringify(ENV_PUBLIC_PATH)});\n` + _
           }
         } else {
           return {

From 8d9234304244b083a333feca5e499c0f94ffc9e5 Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Thu, 16 Dec 2021 22:11:52 +0800
Subject: [PATCH 06/12] Update worker chunk count

---
 packages/playground/worker/__tests__/worker.spec.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/playground/worker/__tests__/worker.spec.ts b/packages/playground/worker/__tests__/worker.spec.ts
index 1fde16117a033e..2d6b695dd5e634 100644
--- a/packages/playground/worker/__tests__/worker.spec.ts
+++ b/packages/playground/worker/__tests__/worker.spec.ts
@@ -57,8 +57,8 @@ if (isBuild) {
   test('inlined code generation', async () => {
     const assetsDir = path.resolve(testDir, 'dist/assets')
     const files = fs.readdirSync(assetsDir)
-    // should have 3 worker chunk
-    expect(files.length).toBe(4)
+    // should have 4 worker chunk
+    expect(files.length).toBe(5)
     const index = files.find((f) => f.includes('index'))
     const content = fs.readFileSync(path.resolve(assetsDir, index), 'utf-8')
     const worker = files.find((f) => f.includes('my-worker'))

From 2605534a24425430d7545b92173b39c873d3d419 Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Thu, 16 Dec 2021 22:14:30 +0800
Subject: [PATCH 07/12] prettier

---
 packages/vite/src/node/plugins/worker.ts | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/packages/vite/src/node/plugins/worker.ts b/packages/vite/src/node/plugins/worker.ts
index a98c216d613a3c..f4369cd0659a58 100644
--- a/packages/vite/src/node/plugins/worker.ts
+++ b/packages/vite/src/node/plugins/worker.ts
@@ -1,4 +1,3 @@
-
 import { ResolvedConfig } from '../config'
 import { Plugin } from '../plugin'
 import { resolvePlugins } from '../plugins'
@@ -44,7 +43,8 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
       if (query && query[WorkerFileId] != null) {
         if (query[ClassicWorkerQuery] != null) {
           return {
-            code: `self.importScripts(${JSON.stringify(ENV_PUBLIC_PATH)});\n` + _
+            code:
+              `self.importScripts(${JSON.stringify(ENV_PUBLIC_PATH)});\n` + _
           }
         } else {
           return {
@@ -98,7 +98,8 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
                 objURL && (window.URL || window.webkitURL).revokeObjectURL(objURL);
               }
             }`
-        } else { // isBuild: true, inline: false
+        } else {
+          // isBuild: true, inline: false
           const basename = path.parse(cleanUrl(id)).name
           const contentHash = getAssetHash(content)
           const fileName = path.posix.join(
@@ -118,7 +119,8 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
             )
           }`
         }
-      } else { // isBuild: false
+      } else {
+        // isBuild: false
         let url = await fileToUrl(cleanUrl(id), config, this)
         url = injectQuery(url, WorkerFileId)
 
@@ -131,7 +133,6 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
           return new ${workerConstructor}(url, workerOptions)
         }`
       }
-
     }
   }
 }

From f0634d0f43e19095cc1584af1d701930af173ebe Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Thu, 16 Dec 2021 22:31:26 +0800
Subject: [PATCH 08/12] Improve workflow & add comment

---
 packages/vite/src/node/plugins/worker.ts | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/packages/vite/src/node/plugins/worker.ts b/packages/vite/src/node/plugins/worker.ts
index f4369cd0659a58..d3fc8616d29446 100644
--- a/packages/vite/src/node/plugins/worker.ts
+++ b/packages/vite/src/node/plugins/worker.ts
@@ -20,6 +20,11 @@ function parseWorkerRequest(id: string): Record<string, string> | null {
 const WorkerFileId = 'worker_file'
 const ClassicWorkerQuery = 'classic'
 
+const esImportEnv = `import ${JSON.stringify(ENV_PUBLIC_PATH)}\n`
+const classicImportEnv = `self.importScripts(${JSON.stringify(
+  ENV_PUBLIC_PATH
+)});\n`
+
 export function webWorkerPlugin(config: ResolvedConfig): Plugin {
   const isBuild = config.command === 'build'
 
@@ -41,15 +46,13 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
     async transform(_, id) {
       const query = parseWorkerRequest(id)
       if (query && query[WorkerFileId] != null) {
-        if (query[ClassicWorkerQuery] != null) {
-          return {
-            code:
-              `self.importScripts(${JSON.stringify(ENV_PUBLIC_PATH)});\n` + _
-          }
-        } else {
-          return {
-            code: `import '${ENV_PUBLIC_PATH}'\n` + _
-          }
+        // For classic workers where `import` is unavailable, we use `importScripts` to inject env.
+        // Note that `importScripts` is not suitable for module workers, because imported modules
+        // would be executed before the env script.
+        const importEnvCode =
+          query[ClassicWorkerQuery] != null ? classicImportEnv : esImportEnv
+        return {
+          code: importEnvCode + _
         }
       }
       if (

From 5f1a4414c6e4d6524e33acaf467c196bc15d2f50 Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Thu, 16 Dec 2021 22:44:20 +0800
Subject: [PATCH 09/12] Update comments

---
 packages/vite/src/node/plugins/worker.ts | 2 --
 1 file changed, 2 deletions(-)

diff --git a/packages/vite/src/node/plugins/worker.ts b/packages/vite/src/node/plugins/worker.ts
index d3fc8616d29446..b54a31e49a4f87 100644
--- a/packages/vite/src/node/plugins/worker.ts
+++ b/packages/vite/src/node/plugins/worker.ts
@@ -47,8 +47,6 @@ export function webWorkerPlugin(config: ResolvedConfig): Plugin {
       const query = parseWorkerRequest(id)
       if (query && query[WorkerFileId] != null) {
         // For classic workers where `import` is unavailable, we use `importScripts` to inject env.
-        // Note that `importScripts` is not suitable for module workers, because imported modules
-        // would be executed before the env script.
         const importEnvCode =
           query[ClassicWorkerQuery] != null ? classicImportEnv : esImportEnv
         return {

From 3684880d30ce0305fd238e9aa81c373c231e7bff Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Thu, 16 Dec 2021 23:02:02 +0800
Subject: [PATCH 10/12] Check worker type in classic worker test

---
 packages/playground/worker/classic-worker.ts | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/packages/playground/worker/classic-worker.ts b/packages/playground/worker/classic-worker.ts
index 7f7e55b1a9c542..fdc7fb7c132778 100644
--- a/packages/playground/worker/classic-worker.ts
+++ b/packages/playground/worker/classic-worker.ts
@@ -1,5 +1,7 @@
 self.onmessage = (e) => {
   if (e.data === 'ping') {
+    // Ensure that we are not in a module worker (calling importScripts in module workers throws an error).
+    self.importScripts();
     self.postMessage('pong')
   }
 }

From 633da271c5446ede6161b646a5bc7d6c438d86bd Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Thu, 16 Dec 2021 23:14:21 +0800
Subject: [PATCH 11/12] prettier

---
 packages/playground/worker/classic-worker.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/playground/worker/classic-worker.ts b/packages/playground/worker/classic-worker.ts
index fdc7fb7c132778..bd6a3b8bbcc600 100644
--- a/packages/playground/worker/classic-worker.ts
+++ b/packages/playground/worker/classic-worker.ts
@@ -1,7 +1,7 @@
 self.onmessage = (e) => {
   if (e.data === 'ping') {
     // Ensure that we are not in a module worker (calling importScripts in module workers throws an error).
-    self.importScripts();
+    self.importScripts()
     self.postMessage('pong')
   }
 }

From e945eca10e559966be4d7b86f2d90e164f5ab018 Mon Sep 17 00:00:00 2001
From: patr0nus <dk4rest@gmail.com>
Date: Fri, 17 Dec 2021 00:22:38 +0800
Subject: [PATCH 12/12] Update docs

---
 docs/guide/features.md | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/docs/guide/features.md b/docs/guide/features.md
index d46b3cdcc80f23..6fe942e7721e1b 100644
--- a/docs/guide/features.md
+++ b/docs/guide/features.md
@@ -336,14 +336,27 @@ import MyWorker from './worker?worker'
 const worker = new MyWorker()
 ```
 
-The worker script can also use `import` statements instead of `importScripts()` - note during dev this relies on browser native support and currently only works in Chrome, but for the production build it is compiled away.
-
 By default, the worker script will be emitted as a separate chunk in the production build. If you wish to inline the worker as base64 strings, add the `inline` query:
 
 ```js
 import MyWorker from './worker?worker&inline'
 ```
 
+The custom worker constructor accepts an optional parameter `options`. It will be passed as the second parameter to the [`Worker`](http://developer.mozilla.org/en-US/docs/Web/API/Worker/Worker) constructor, with the caveat that the default value of field `type` is `"module"`, so if you wish to create a classic worker, `{ type: "classic" }` must be explicity passed:
+
+```js
+import MyClassicWorker from './classic-worker?worker'
+
+const worker = new MyClassicWorker({ type: 'classic' })
+```
+
+### Worker Type Comparisons
+
+|                      | Can use `import` | Browser Support During Development                                                              | Browser Support of Production Build |
+| -------------------- | ---------------- | ----------------------------------------------------------------------------------------------- | ----------------------------------- |
+| `"module"` (default) | Yes              | Safari 15+ and Chrome ([caniuse](https://caniuse.com/mdn-api_worker_worker_ecmascript_modules)) | All                                 |
+| `"classic"`          | No               | All                                                                                             | All                                 |
+
 ## Build Optimizations
 
 > Features listed below are automatically applied as part of the build process and there is no need for explicit configuration unless you want to disable them.