mochajs/mocha · error · TypeError

ERR_MOCHA_INVALID_ARG_TYPE

ERR_MOCHA_INVALID_ARG_TYPE

Error message

Mocha flag '${flag}' given invalid option: '${numericArg}'

What it means

Error "Mocha flag '${flag}' given invalid option: '${numericArg}'" thrown in mochajs/mocha.

Source

Thrown at lib/cli/parse-args.js:364

  numericArg,
  allArgs,
  parsedResult,
) => {
  // A flag for `numericArg` exists if:
  // 1. A Mocha flag immediately preceded the numericArg in `allArgs`, and
  // 2. parseArgs() could not assign the numericArg to that flag because the
  //    option has an incompatible datatype.
  const flag = allArgs.find((arg, index) => {
    const normalizedArg = stripLeadingDashes(arg);
    return (
      isMochaFlag(arg) &&
      allArgs[index + 1] === String(numericArg) &&
      parsedResult[normalizedArg] !== String(numericArg)
    );
  });

  if (flag) {
    throw createInvalidArgumentTypeError(
      `Mocha flag '${flag}' given invalid option: '${numericArg}'`,
      numericArg,
      expectedTypeForFlag(flag),
    );
  }

  throw createUnsupportedError(
    `Option ${numericArg} is unsupported by the mocha cli`,
  );
};

/**
 * Parse the args into a config object.
 * Splits,
 * handles Node args,
 * validates general args,
 * parses into config object,
 * normalizes,

View on GitHub (pinned to 6bcbee4fd9)

When it happens

Trigger: Thrown at lib/cli/parse-args.js:364 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of mochajs/mocha@6bcbee4fd9 (2026-09-01). Data as JSON: /api/errors/e156c31760481556. Report an issue: GitHub.