parcel-bundler/parcel · error · Error

Cannot require '${resolved}' in the browser

Error message

Cannot require '${resolved}' in the browser

What it means

Thrown by `BrowserPackageManager.require` in the in-browser Parcel REPL when a resolved module is not in the `BUILTINS` map. The REPL only has the parcel core plugins bundled in; any other package can be resolved by path but cannot actually be `require()`-loaded in the browser sandbox.

Source

Thrown at packages/dev/repl/src/parcel/BrowserPackageManager.js:161

  }

  async require(
    name: DependencySpecifier,
    from: FilePath,
    opts: ?{|
      range?: ?SemverRange,
      shouldAutoInstall?: boolean,
      saveDev?: boolean,
    |},
  ): Promise<any> {
    let {resolved} = await this.resolve(name, from, opts);

    // $FlowFixMe
    if (resolved in BUILTINS) {
      return BUILTINS[resolved];
    }

    throw new Error(`Cannot require '${resolved}' in the browser`);
  }

  async resolve(
    name: DependencySpecifier,
    from: FilePath,
    // eslint-disable-next-line no-unused-vars
    options?: ?{|
      range?: ?SemverRange,
      shouldAutoInstall?: boolean,
      saveDev?: boolean,
    |},
  ): Promise<ResolveResult> {
    if (name.startsWith('@parcel/') && name !== '@parcel/watcher') {
      return Promise.resolve({
        resolved: name,
        pkg: {
          name: name,
          version: '2.0.0',

View on GitHub (pinned to 59484858a1)

Solutions

1. Only reference parcel plugins that ship in the REPL's BUILTINS list (the standard `@parcel/*` set).
2. Remove custom `.parcelrc` entries that pull in third-party plugins when running in the REPL.
3. If you control the REPL build, add the needed package to the BUILTINS map at build time.
4. Run the build with a local Parcel install instead of the in-browser REPL for non-builtin plugins.

Example fix

// before — .parcelrc references a non-bundled plugin
{
  "transformers": { "*.foo": "parcel-transformer-foo" }
}
// after — drop it in the REPL
{ "extends": "@parcel/config-default" }

import { BUILTINS } from '@parcel/repl/.../BrowserPackageManager.js';
function canRequireInRepl(resolved) { return resolved in BUILTINS; }

function isBuiltinPlugin(spec) {
  return typeof spec === 'string' && Object.prototype.hasOwnProperty.call(BUILTINS, spec);
}

When it happens

Trigger: A parcel plugin/config tries to `require()` a package that is not one of the pre-bundled `@parcel/*` plugins; resolving succeeds to a path but the package isn't in `BUILTINS`.

Common situations: REPL loads a project whose parcel config references a custom/third-party plugin or runtime not bundled into the REPL; a transformer tries to require a helper package at runtime.

Related errors

• IDBCache is only supported in the browser
• More than one target is not supported in serve mode
• NodeFS isn't available in the browser
• No dynamic require possible: ${workerPath}
• No dynamic require possible: ${location}

AI-assisted analysis of parcel-bundler/parcel@59484858a1 (2026-08-13). Data as JSON: /api/errors/db1a172ed8bf54d4. Report an issue: GitHub.