diff --git a/.changeset/spicy-panthers-prove.md b/.changeset/spicy-panthers-prove.md
new file mode 100644
index 0000000000..7eb6f352a1
--- /dev/null
+++ b/.changeset/spicy-panthers-prove.md
@@ -0,0 +1,6 @@
+---
+'@shopify/web-worker': minor
+---
+
+- Allow `output.chunkFilename` to be a function or string.
+- `compiler.options.output.filename` and `compiler.options.output.chunkFilename` now default to `[name].js` when undefined.
diff --git a/packages/web-worker/src/webpack-parts/loader.ts b/packages/web-worker/src/webpack-parts/loader.ts
index 505ff5ba2f..83f33915ef 100644
--- a/packages/web-worker/src/webpack-parts/loader.ts
+++ b/packages/web-worker/src/webpack-parts/loader.ts
@@ -78,14 +78,19 @@ export function pitch(this: LoaderContext<Options>, request: string) {
       wrapperContent = cachedContent;
     } else if (cachedContent == null) {
       try {
-        wrapperContent = this.fs.readFileSync(wrapperModule).toString();
-        moduleWrapperCache.set(wrapperModule, wrapperContent ?? false);
+        if (this.fs?.readFileSync) { 
+          wrapperContent = this.fs.readFileSync(wrapperModule).toString();
+          moduleWrapperCache.set(wrapperModule, wrapperContent ?? false);
+        } else {
+          throw new Error("readFileSync is undefined");
+        }
       } catch (error) {
         moduleWrapperCache.set(wrapperModule, false);
       }
     }
   }
 
+
   if (wrapperContent) {
     plugin.virtualModules.writeModule(
       virtualModule,