Can web worker help split Vite result js file?

You’re doing

import dictionary from "./bigDictionary.js";

Proplem

Vite sees this as a static import → so it bundles the dictionary into the main bundle.

Result: your main JavaScript file = React App + dictionary (28 MB).

If you move it to a Web Worker

The Web Worker file is built as a separate file in Vite.

When you do:

new Worker(new URL("./worker.js", import.meta.url))

Vite outputs worker.js as a separate file.

Any import inside worker.js (like your 28 MB dictionary) will be bundled into the worker file, not the main bundle.

Result:

Main bundle stays small (without the dictionary).

Worker bundle contains the dictionary.

The worker file is only downloaded when you create the worker.

So yes, this way the dictionary is separated from the main code.

// main.tsx
const worker = new Worker(new URL("./worker.js", import.meta.url), { type: "module" });

worker.postMessage("getDict");
worker.onmessage = (e) => {
  console.log("Dictionary received:", e.data);
};

// worker.js
import dictionary from "./bigDictionary.js";

self.onmessage = (e) => {
  if (e.data === "getDict") {
    postMessage(dictionary);
  }
};

Result:

index.js (main bundle, small)

worker.js (separate ~28 MB file, downloaded only when the worker is created)

Important notes

When you send a large object from the worker to the main thread → structured cloning happens (the browser makes a full copy of the object), which can be heavy for memory and performance.

Since the dictionary is 28 MB, it’s usually better to:

Keep it as a JSON file and fetch it only when needed:

const dict = await fetch("/dict.json").then(r => r.json());

Or store it in IndexedDB so it doesn’t reload every time.

If you need to run heavy searches or processing on the dictionary → then a worker is really useful.

Summary: Yes, moving the dictionary to a Web Worker makes Vite build it as a separate file and reduces the main bundle size. But if your only goal is to shrink the bundle, the simplest and more efficient solution is to keep the dictionary as a JSON file and fetch it instead of bundling it into your code.