THIS_IS_UNDEFINED warning persists on Rollup entry points despite context and moduleContext options

The Short Answer

There is no configuration option in Rollup 4.x that allows context or moduleContext to override the this binding for the outermost entry point wrapper. Because Rollup enforces strict mode for ES modules, the top-level this is intentionally undefined. To resolve this, you must replace top-level references to this with globalThis.

Why Configuration Options Fail

The context and moduleContext options are designed to provide a specific value for this inside the function wrappers that Rollup uses to isolate individual modules. However, the entry point's execution context is governed by the output format (e.g., ESM, CJS, IIFE) and the strict mode requirements of the JavaScript engine.

When Rollup detects a top-level this in a module that will be executed in strict mode, it issues the THIS_IS_UNDEFINED warning. Since this is a fundamental behavior of the JS engine's strict mode, a build-time configuration cannot "force" the runtime to bind this to the global object without breaking the module's strictness.

Recommended Resolution

The industry-standard approach for modern JavaScript (Node.js 12+ and all modern browsers) is to use globalThis. This provides a consistent way to access the global scope regardless of the environment or module wrapper.

Implementation Steps

1. Identify the reference: Locate the top-level this usage in your entry point.
2. Replace with globalThis:

   // Change this:
   const global = this;
   
   // To this:
   const global = globalThis;

3. Verify the bundle: Run your build and confirm the THIS_IS_UNDEFINED warning has disappeared from the console.

Alternative for Legacy Environments

If you must support environments where globalThis is unavailable, use a polyfill or a conditional check:

const root = typeof globalThis !== 'undefined' ? globalThis : (typeof window !== 'undefined' ? window : global);

Verification

To confirm the fix, you can add a temporary log to your entry point and run the bundle in your target environment:

console.log('Global context check:', globalThis);

If you are using a non-standard output format or a specific plugin that modifies the wrapper, please specify the output.format used in your rollup.config.js, as this may change the runtime behavior of the wrapper.