mochajs/mocha · error · Error

ERR_MOCHA_UNPARSABLE_FILE

ERR_MOCHA_UNPARSABLE_FILE

Error message

Unable to read/parse ${filepath}: ${err}

What it means

When Mocha loads a JS/JSON config file (.mocharc.js/.mjs/cjs or .mocharc.json) it wraps parsing in try/catch; any read or parse failure is rethrown as ERR_MOCHA_UNPARSABLE_FILE with the original error embedded. This tells you exactly which config file Mocha could not load instead of leaking a low-level require/JSON error.

Source

Thrown at lib/cli/config.cjs:84

 * @param {string} filepath - Config file path to load
 * @returns {Object} Parsed config object
 */
exports.loadConfig = (filepath) => {
  let config;
  debug("loadConfig: trying to parse config at %s", filepath);

  const ext = path.extname(filepath);
  try {
    if (ext === ".yml" || ext === ".yaml") {
      config = parsers.yaml(filepath);
    } else if (ext === ".js" || ext === ".cjs" || ext === ".mjs") {
      const parsedConfig = parsers.js(filepath);
      config = parsedConfig.default ?? parsedConfig;
    } else {
      config = parsers.json(filepath);
    }
  } catch (err) {
    throw createUnparsableFileError(
      `Unable to read/parse ${filepath}: ${err}`,
      filepath,
    );
  }
  return config;
};

/**
 * Find ("find up") config file starting at `cwd`
 *
 * @param {string} [cwd] - Current working directory
 * @returns {string|null} Filepath to config, if found
 */
exports.findConfig = (cwd = utils.cwd()) => {
  const filepath = findUp.sync(exports.CONFIG_FILES, { cwd });
  if (filepath) {
    debug("findConfig: found config file %s", filepath);
  }

View on GitHub (pinned to 6bcbee4fd9)

Solutions

1. Open the mocharc file cited in the message and fix the underlying syntax/import error shown after the colon.
2. Validate the file standalone: `node -e "require('./.mocharc.js')"` (or JSON.parse for json).
3. If using ESM syntax, rename to .mocharc.mjs or ensure your Node version supports it.
4. Restore the file from version control or fix file permissions.

Example fix

// before (.mocharc.js)
module.exports = {spec: 'test/*.spec.js',,}; // syntax error
// after
module.exports = {spec: 'test/*.spec.js'};

const configPath = './.mocharc.js';
try {
  const cfg = require(require('path').resolve(configPath));
  console.log('config OK', Object.keys(cfg));
} catch (err) {
  console.error(`Invalid mocharc: ${err.message}`); // fix before running mocha
}

function isLoadableConfig(p) {
  try { require(require('path').resolve(p)); return true; } catch { return false; }
}

try {
  execSync('npx mocha', {stdio: 'inherit'});
} catch (err) {
  if (String(err.stderr).includes('ERR_MOCHA_UNPARSABLE_FILE')) {
    console.error('Fix the mocharc file cited in the error output');
  }
}

When it happens

Trigger: Running mocha with a .mocharc.js/.mocharc.json that has a syntax error, uses unsupported syntax (e.g. ESM in .js on old Node), throws at import time, or is unreadable on disk.

Common situations: Hand-editing mocharc and leaving a trailing comma; committing a config referencing missing imports; a .mocharc.js that executes code failing at load; permission problems on the config file.

Related errors

• ERR_MOCHA_UNPARSABLE_FILE
• Not enough non-option arguments: got 0, need at least 1
• Not enough arguments following: ${name}
• Warning: ${warning.message}
• ERR_MOCHA_NO_FILES_MATCH_PATTERN

AI-assisted analysis of mochajs/mocha@6bcbee4fd9 (2026-09-01). Data as JSON: /api/errors/a2dc6d7a0407499f. Report an issue: GitHub.