parcel-bundler/parcel · error · ThrowableDiagnostic

Config result is not hashable because it contains non-serial

Error message

Config result is not hashable because it contains non-serializable objects. Please use config.setCacheKey to set the hash manually.

What it means

To cache a config result, Parcel hashes it. When `config.cacheKey` is null and `config.result` is non-null, it tries `serializeRaw(config.result)`. If the result contains non-serializable values (functions, class instances, symbols, circular structures), serialization throws and Parcel wraps it in this diagnostic telling you to set a manual cache key.

Source

Thrown at packages/core/core/src/requests/ConfigRequest.js:245

  // If there is no result hash set by the transformer, default to hashing the included
  // files if any, otherwise try to hash the config result itself.
  if (config.cacheKey == null) {
    if (config.invalidateOnFileChange.size > 0) {
      hash.writeString(
        await getInvalidationHash(
          [...config.invalidateOnFileChange].map(filePath => ({
            type: 'file',
            filePath,
          })),
          options,
        ),
      );
    } else if (config.result != null) {
      try {
        hash.writeBuffer(serializeRaw(config.result));
      } catch (err) {
        throw new ThrowableDiagnostic({
          diagnostic: {
            message:
              'Config result is not hashable because it contains non-serializable objects. Please use config.setCacheKey to set the hash manually.',
            origin: pluginName,
          },
        });
      }
    }
  } else {
    hash.writeString(config.cacheKey ?? '');
  }

  return hash.finish();
}

export function getConfigRequests(
  configs: Array<Config>,
): Array<ConfigRequest> {

View on GitHub (pinned to 59484858a1)

Solutions

Call `config.setCacheKey(manualHash)` with a stable string derived from the config inputs.
Return only JSON-serializable data (strings, numbers, plain objects/arrays).
If you must return non-serializable objects, store them out-of-band and return a reference/key, then hash the source.

Example fix

// before
config.setResult({ match: new RegExp(pattern) });

// after
config.setResult({ pattern });
config.setCacheKey(createHash(pattern));

Defensive patterns

Strategy: validation

Validate before calling

// If the result isn't serializable, set a manual cache key.
try {
  serializeRaw(config.result);
} catch {
  config.setCacheKey(createHashFromInputs(config));
}

Type guard

function isSerializable(value: mixed): boolean {
  try { JSON.stringify(value); return true; } catch { return false; }
}

Try / catch

try {
  await serializeRaw(config.result);
} catch (err) {
  config.setCacheKey(manualHash);
}

Prevention

Return only JSON-serializable config results when possible.
Call config.setCacheKey() whenever you return functions, regexes, or class instances.
Derive the manual key from stable inputs (file contents, versions), not runtime state.

When it happens

Trigger: A config plugin returns a result object that contains functions, class instances, or other non-plain-serializable data, and does not call `config.setCacheKey()`.

Common situations: Config loaders that return compiled regexes, function factories, or third-party class instances; configs that capture closures.

Related errors

AI-assisted analysis of parcel-bundler/parcel@59484858a1 (2026-08-13). Data as JSON: /api/errors/7d988a592e0f478a. Report an issue: GitHub.