Node ERR_INVALID_ARG_TYPE in CI - Pass the Right Argument Type

By Kaveh Alemi·Latchkey

ERR_INVALID_ARG_TYPE is thrown by Node core APIs when you pass an argument of the wrong type, most often undefined where a string or Buffer was required.

What this error means

A node process throws TypeError [ERR_INVALID_ARG_TYPE], for example "The path argument must be of type string. Received undefined", at a core API call.

TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type
string or an instance of Buffer or URL. Received undefined
    at Object.readFileSync (node:fs:451:10) {
  code: 'ERR_INVALID_ARG_TYPE'
}

Common causes

A missing environment variable resolved to undefined

A path or value derived from an env var that is unset in CI becomes undefined and is passed straight to a core API.

A function returned undefined where a value was expected

An upstream call returned nothing, and that undefined flowed into a strict core API.

How to fix it

Validate inputs before the core call

1. Assert the argument is defined and the right type before passing it.
2. Fail with a clear message if the input is missing.

if (typeof path !== 'string') {
  throw new Error('CONFIG_PATH is not set');
}

Set the missing CI environment variable

1. Confirm which env var the argument depends on.
2. Provide it in the workflow env for the failing step.

- run: node build.js
  env:
    CONFIG_PATH: ./config/ci.json

How to prevent it

• Validate external inputs and env-derived values at the boundary, and use TypeScript or schema checks so undefined cannot silently reach a core API.

Frequently asked questions

Related guides

References

• Node.js documentation
• npm CLI documentation
• GitHub Actions documentation