jestjs/jest · error · Error

The first argument to require.resolve must be a string. Rece

Error message

The first argument to require.resolve must be a string. Received null or undefined.

What it means

Thrown by `RequireBuilder.resolve` (cjsRequire.ts:112-121) when `require.resolve` is called with `null` or `undefined`. The runtime guards `moduleName == null` before doing any path work because every downstream step assumes a string.

Source

Thrown at packages/jest-runtime/src/internals/cjsRequire.ts:118

        children: [],
        exports: {},
        filename,
        id: filename,
        isPreloading: false,
        loaded: false,
        path: path.dirname(filename),
      },
      undefined,
    );
  }

  private resolve(
    from: string,
    moduleName: string | undefined,
    options: ResolveOptions = {},
  ): string {
    if (moduleName == null) {
      throw new Error(
        'The first argument to require.resolve must be a string. Received null or undefined.',
      );
    }

    if (path.isAbsolute(moduleName)) {
      const module = this.resolution.resolveCjsFromDirIfExists(
        moduleName,
        moduleName,
        [],
      );
      if (module) {
        return module;
      }
    } else if (options.paths) {
      const module = this.resolution.resolveCjsStub(from, moduleName);

      if (module) {
        return module;

View on GitHub (pinned to f49721c78e)

Solutions

1. Ensure the argument is a string before calling: `if (typeof name === 'string') require.resolve(name)`.
2. Default the variable: `const name = process.env.MODULE ?? 'fallback'; require.resolve(name);`.
3. Add a precondition check at the boundary that produced the null/undefined.

Example fix

// before
require.resolve(process.env.TARGET_MODULE); // throws if unset

// after
const target = process.env.TARGET_MODULE;
if (typeof target === 'string') require.resolve(target);
else throw new Error('TARGET_MODULE must be set');

if (typeof name !== 'string' || name.length === 0) {
  throw new Error('require.resolve needs a non-empty string');
}
require.resolve(name);

function isNonEmptyString(v: unknown): v is string {
  return typeof v === 'string' && v.length > 0;
}

When it happens

Trigger: `require.resolve(null)`, `require.resolve(undefined)`, or `require.resolve(someVar)` where `someVar` was never assigned. Dynamic builds of the module name that occasionally yield `null`.

Common situations: Config-driven code where a path comes from an optional env var that wasn't set. Refactors that pass `moduleName` through optional chaining.

Related errors

• The first argument to require.resolve.paths must be a string
• The first argument to require.resolve.paths must not be the
• @jest/diff-sequences: ${name} typeof ${typeof arg} is not a
• @jest/diff-sequences: ${name} value ${arg} is not a safe int
• @jest/diff-sequences: ${name} value ${arg} is a negative int

AI-assisted analysis of jestjs/jest@f49721c78e (2026-08-03). Data as JSON: /data/errors/846158abff1730f3.json. Report an issue: GitHub.