parcel-bundler/parcel · error · Error

No dynamic require possible: ${workerPath}

Error message

No dynamic require possible: ${workerPath}

What it means

Thrown by WorkerFarm when process.browser is true (running in a browser bundle) and options.workerPath is not the one allowed browser entry '@parcel/core/src/worker.js'. In a browser there is no dynamic require, so only the pre-bundled coreWorker reference is permitted; any other path is rejected.

Source

Thrown at packages/core/workers/src/WorkerFarm.js:111

        farmOptions.shouldTrace ? 1 : DEFAULT_MAX_CONCURRENT_CALLS,
      ),
      forcedKillTime: 500,
      warmWorkers: false,
      useLocalWorker: true, // TODO: setting this to false makes some tests fail, figure out why
      backend: detectBackend(),
      ...farmOptions,
    };

    if (!this.options.workerPath) {
      throw new Error('Please provide a worker path!');
    }

    // $FlowFixMe
    if (process.browser) {
      if (this.options.workerPath === '@parcel/core/src/worker.js') {
        this.localWorker = coreWorker;
      } else {
        throw new Error(
          'No dynamic require possible: ' + this.options.workerPath,
        );
      }
    } else {
      // $FlowFixMe this must be dynamic
      this.localWorker = require(this.options.workerPath);
    }

    this.localWorkerInit =
      this.localWorker.childInit != null ? this.localWorker.childInit() : null;

    this.run = this.createHandle('run');

    // Worker thread stdout is by default piped into the process stdout, if there are enough worker
    // threads to exceed the default listener limit, then anything else piping into stdout will trigger
    // the `MaxListenersExceededWarning`, so we should ensure the max listeners is at least equal to the
    // number of workers + 1 for the main thread.
    //

View on GitHub (pinned to 59484858a1)

Solutions

1. In browser builds, leave workerPath unset or set it to '@parcel/core/src/worker.js' so the pre-bundled coreWorker is used.
2. Avoid bundling @parcel/workers into browser code unless you specifically support the web worker backend.
3. Use the 'web' worker backend and ensure the bundler exposes coreWorker via the expected module id.

Example fix

// before (browser bundle)
new WorkerFarm({ workerPath: './myWorker.js' });

// after
new WorkerFarm({ workerPath: '@parcel/core/src/worker.js' });

if (process.browser && options.workerPath !== '@parcel/core/src/worker.js') {
  throw new Error('In browser builds only the bundled core worker path is allowed.');
}

When it happens

Trigger: Bundling @parcel/workers for the browser (e.g. with webpack/rollup) and setting workerPath to a custom module; running Parcel's worker code in a browser context that is not the bundled core worker.

Common situations: Reusing @parcel/workers in a browser/web worker toolchain; accidentally including Parcel's worker code in a web bundle via a misconfigured bundler; web-based Parcel playgrounds.

Related errors

• No dynamic require possible: ${location}
• No dynamic require possible: ${module}
• Please provide a worker path!
• IDBCache is only supported in the browser
• Supplied WorkerFarm is ending

AI-assisted analysis of parcel-bundler/parcel@59484858a1 (2026-08-13). Data as JSON: /api/errors/94561f404071169d. Report an issue: GitHub.