What causes "name argument is required to req.get" in expressjs/express?

Pass an explicit header name string, e.g. req.get('content-type').

expressjs/express · error · TypeError

name argument is required to req.get

Error message

name argument is required to req.get

What it means

Express's req.get() (aliased req.header()) reads a request header by name. At lib/request.js:65-67 it throws a TypeError when the name argument is falsy (undefined, null, or empty string), because looking up a header without a name is always a programming mistake rather than a runtime condition Express can recover from.

Source

Thrown at lib/request.js:66

 *     // => "text/plain"
 *
 *     req.get('content-type');
 *     // => "text/plain"
 *
 *     req.get('Something');
 *     // => undefined
 *
 * Aliased as `req.header()`.
 *
 * @param {String} name
 * @return {String}
 * @public
 */

req.get =
req.header = function header(name) {
  if (!name) {
    throw new TypeError('name argument is required to req.get');
  }

  if (typeof name !== 'string') {
    throw new TypeError('name must be a string to req.get');
  }

  var lc = name.toLowerCase();

  switch (lc) {
    case 'referer':
    case 'referrer':
      return this.headers.referrer
        || this.headers.referer;
    default:
      return this.headers[lc];
  }
};

View on GitHub ↗ (pinned to a3714473fe)

Solutions

Pass an explicit header name string, e.g. req.get('content-type').
Trace where the argument comes from and guard against the config value being undefined (fail fast at startup if a required header name isn't configured).
If you want all headers, use req.headers directly instead of req.get().

Example fix

// before
const auth = req.get(process.env.AUTH_HEADER); // AUTH_HEADER unset -> undefined
// after
const headerName = process.env.AUTH_HEADER;
if (!headerName) throw new Error('AUTH_HEADER env var is required');
const auth = req.get(headerName);

Defensive patterns

Strategy: validation

Validate before calling

if (headerName === undefined || headerName === null) {
  throw new Error('header name is required before calling req.get');
}
const value = req.get(headerName);

Type guard

function hasHeaderName(name) {
  return name !== undefined && name !== null;
}

Try / catch

try {
  const value = req.get(headerName);
} catch (err) {
  if (/name argument is required/.test(err.message)) {
    // caller passed undefined/null — fix the call site
  }
  throw err;
}

Prevention

Never pass a variable to req.get() without checking it is defined — undefined header names usually come from optional config or destructuring typos.
Use a constant for header names (e.g. const HDR_AUTH = 'authorization') instead of building them dynamically.
Add a lint rule or wrapper helper that asserts the header name is present before delegating to req.get.

When it happens

Trigger: Calling req.get() or req.header() with no argument, or passing a variable that evaluates to undefined/null/'' — e.g. req.get(config.headerName) where headerName was never set, or req.get() during a refactor that dropped the argument.

Common situations: Header names sourced from environment variables or config objects that are missing in a deployment environment; destructured options with a typo'd key; code migrated from frameworks where a no-arg call returned all headers. Note Express 4 threw the same error, so this is rarely a version-upgrade issue.

Related errors

AI-assisted analysis of expressjs/express@a3714473fe (2026-07-31). Data as JSON: /data/errors/03e58cd4b5b895ac.json. Report an issue: GitHub ↗.