GoogleChrome/lighthouse · error

UIStrings defined in file but not exported

Error message

UIStrings defined in file but not exported

What it means

Thrown during collection when the UISTRINGS_REGEX finds a UIStrings definition in the file text, but the module's runtime exports do not actually include UIStrings. The scanner found something that looks like a definition but it isn't exported, so messages cannot be correlated with runtime values for example/placeholder extraction.

Source

Thrown at core/scripts/i18n/collect-strings.js:586

  for (const relativeToRootPath of files) {
    const absolutePath = path.join(LH_ROOT, relativeToRootPath);
    if (!process.env.CI) console.log('Collecting from', relativeToRootPath);

    const content = fs.readFileSync(absolutePath, 'utf8');
    const exportVars = await import(pathToFileURL(absolutePath).href);
    const regexMatch = content.match(UISTRINGS_REGEX);
    const exportedUIStrings = exportVars.UIStrings || exportVars.default?.UIStrings;

    if (!regexMatch) {
      // No UIStrings found in the file text or exports, so move to the next.
      if (!exportedUIStrings) continue;

      throw new Error('UIStrings exported but no definition found: ' + relativeToRootPath);
    }

    if (!exportedUIStrings) {
      throw new Error('UIStrings defined in file but not exported');
    }

    // just parse the UIStrings substring to avoid ES version issues, save time, etc
    const justUIStrings = 'const ' + regexMatch[0];
    const parsedMessages = parseUIStrings(justUIStrings, exportedUIStrings);

    for (const [key, parsed] of Object.entries(parsedMessages)) {
      const {message, description, examples} = parsed;
      const converted = convertMessageToCtc(message, examples);

      // Don't include placeholders if there are none.
      const placeholders = Object.keys(converted.placeholders).length === 0 ?
          undefined :
          converted.placeholders;

      /** @type {CtcMessage} */
      const ctc = {
        message: converted.message,

View on GitHub (pinned to 9515cd4e58)

Solutions

1. Add `export` to the UIStrings definition: `export const UIStrings = {...}`.
2. Ensure the exported name is exactly `UIStrings`.
3. Confirm there is only one UIStrings definition and it is the one being exported.

Example fix

// before
const UIStrings = {
  myMessage: 'My message',
};
// after
export const UIStrings = {
  myMessage: 'My message',
};

function isUIStringsExported(moduleExports) {
  return Boolean(moduleExports.UIStrings || moduleExports.default?.UIStrings);
}

When it happens

Trigger: Defining `const UIStrings = {...}` in a file but forgetting the `export` keyword, or exporting it under a different name than `UIStrings`.

Common situations: Forgetting to add `export`; renaming the export but not the definition; defining UIStrings inside a function scope so it isn't a module-level export.

Related errors

• UIStrings exported but no definition found: ${relativeToRoot
• unsupported JSDoc comment: ${JSON.stringify(comment)}
• Incorrectly formatted @example: "${rawExample}"
• [${err.message}] Did not find the expected syntax in message
• Content cannot appear outside plural or select ICU messages.

AI-assisted analysis of GoogleChrome/lighthouse@9515cd4e58 (2026-08-13). Data as JSON: /api/errors/da955a16c3463918. Report an issue: GitHub.