2 files changed, 66 insertions, 11 deletions

diff --git a/runtime/js/11_workers.js b/runtime/js/11_workers.js
index b5a8a9d0c..2f9413119 100644
--- a/runtime/js/11_workers.js
+++ b/runtime/js/11_workers.js
@@ -7,7 +7,6 @@
     ArrayIsArray,
     ArrayPrototypeMap,
     Error,
-    Uint8Array,
     StringPrototypeStartsWith,
     String,
     SymbolIterator,
@@ -28,6 +27,7 @@
     useDenoNamespace,
     permissions,
     name,
+    workerType,
   ) {
     return core.opSync("op_create_worker", {
       hasSourceCode,
@@ -36,6 +36,7 @@
       sourceCode,
       specifier,
       useDenoNamespace,
+      workerType,
     });
   }
 
@@ -183,20 +184,12 @@
         }
       }
 
-      if (type !== "module") {
-        throw new Error(
-          'Not yet implemented: only "module" type workers are supported',
-        );
-      }
-
-      this.#name = name;
-      const hasSourceCode = false;
-      const sourceCode = core.decode(new Uint8Array());
+      const workerType = webidl.converters["WorkerType"](type);
 
       if (
         StringPrototypeStartsWith(specifier, "./") ||
         StringPrototypeStartsWith(specifier, "../") ||
-        StringPrototypeStartsWith(specifier, "/") || type == "classic"
+        StringPrototypeStartsWith(specifier, "/") || workerType === "classic"
       ) {
         const baseUrl = getLocationHref();
         if (baseUrl != null) {
@@ -204,6 +197,16 @@
         }
       }
 
+      this.#name = name;
+      let hasSourceCode, sourceCode;
+      if (workerType === "classic") {
+        hasSourceCode = true;
+        sourceCode = `importScripts("#");`;
+      } else {
+        hasSourceCode = false;
+        sourceCode = "";
+      }
+
       const id = createWorker(
         specifier,
         hasSourceCode,
@@ -213,6 +216,7 @@
           ? null
           : parsePermissions(workerDenoAttributes.permissions),
         options?.name,
+        workerType,
       );
       this.#id = id;
       this.#pollControl();
@@ -344,6 +348,11 @@
   defineEventHandler(Worker.prototype, "message");
   defineEventHandler(Worker.prototype, "messageerror");
 
+  webidl.converters["WorkerType"] = webidl.createEnumConverter("WorkerType", [
+    "classic",
+    "module",
+  ]);
+
   window.__bootstrap.worker = {
     parsePermissions,
     Worker,
diff --git a/runtime/js/99_main.js b/runtime/js/99_main.js
index 6d5599e71..b1f7d1473 100644
--- a/runtime/js/99_main.js
+++ b/runtime/js/99_main.js
@@ -8,6 +8,7 @@ delete Object.prototype.__proto__;
 ((window) => {
   const core = Deno.core;
   const {
+    ArrayPrototypeMap,
     Error,
     FunctionPrototypeCall,
     FunctionPrototypeBind,
@@ -164,6 +165,44 @@ delete Object.prototype.__proto__;
     }
   }
 
+  let loadedMainWorkerScript = false;
+
+  function importScripts(...urls) {
+    if (core.opSync("op_worker_get_type") === "module") {
+      throw new TypeError("Can't import scripts in a module worker.");
+    }
+
+    const baseUrl = location.getLocationHref();
+    const parsedUrls = ArrayPrototypeMap(urls, (scriptUrl) => {
+      try {
+        return new url.URL(scriptUrl, baseUrl ?? undefined).href;
+      } catch {
+        throw new domException.DOMException(
+          "Failed to parse URL.",
+          "SyntaxError",
+        );
+      }
+    });
+
+    // A classic worker's main script has looser MIME type checks than any
+    // imported scripts, so we use `loadedMainWorkerScript` to distinguish them.
+    // TODO(andreubotella) Refactor worker creation so the main script isn't
+    // loaded with `importScripts()`.
+    const scripts = core.opSync(
+      "op_worker_sync_fetch",
+      parsedUrls,
+      !loadedMainWorkerScript,
+    );
+    loadedMainWorkerScript = true;
+
+    for (const { url, script } of scripts) {
+      const err = core.evalContext(script, url)[1];
+      if (err !== null) {
+        throw err.thrown;
+      }
+    }
+  }
+
   function opMainModule() {
     return core.opSync("op_main_module");
   }
@@ -597,6 +636,13 @@ delete Object.prototype.__proto__;
     }
     ObjectDefineProperties(globalThis, workerRuntimeGlobalProperties);
     ObjectDefineProperties(globalThis, { name: util.readOnly(name) });
+    if (runtimeOptions.enableTestingFeaturesFlag) {
+      ObjectDefineProperty(
+        globalThis,
+        "importScripts",
+        util.writable(importScripts),
+      );
+    }
     ObjectSetPrototypeOf(globalThis, DedicatedWorkerGlobalScope.prototype);
 
     const consoleFromDeno = globalThis.console;