Implicit Globals vs Declaration Enforcement: no‑implicit‑globals vs no‑var

Direct Answer

no-implicit-globals is intended for scripts, where a top-level function declaration becomes a property of the global object. In ES modules, top-level declarations are module-scoped and do not leak to the global object, so the rule’s premise does not apply. Nevertheless, some ESLint versions still report these declarations because the implementation inspects Program-level nodes without consulting languageOptions.sourceType. For a module-only project, the practical resolution is to disable no-implicit-globals. Do not treat no-var as a replacement; it enforces let/const and does not address global leakage.

Likely Explanation vs. Confirmed Facts

Confirmed: The rule documentation describes a script-oriented goal, and no-var is a separate stylistic rule with no bearing on global scope.

Version-dependent: Whether your installed ESLint flags module top-level functions depends on implementation details. Historically, the rule has not checked sourceType automatically, but exact behavior can vary by major version and parser configuration. Any change to auto-detect modules should be treated as version-specific until verified.

Steps for This Case

1. Verify the effective configuration for a representative module file:

   eslint --print-config src/example.js

   Confirm that languageOptions.sourceType is "module" and that no-implicit-globals is active.
2. Create a minimal reproduction file with a top-level function declaration and lint it:

   // repro.js
   function helper() {}
   export default helper;

   Run ESLint against the file to see if the rule reports the declaration.
3. If the warning appears in a module-only codebase, disable the rule in your ESLint configuration. If you maintain mixed script and module files, scope the disable to module files using configuration overrides rather than turning it off globally.
4. Keep no-var enabled only if you want let/const enforcement; it solves a different problem.

Future Releases and Tracking

There is no confirmed knowledge that ESLint has modified no-implicit-globals to detect sourceType automatically in a specific release. Treat any such change as version-specific and verify against your installed version’s rule source or changelog. I cannot confirm the existence of a specific open issue tracking this ambiguity; avoid citing one without direct verification.

Missing Diagnostic Detail

Which ESLint major version are you running? The answer determines whether the rule actually fires in your environment and whether the configuration override is necessary.