unambiguous.md

import/unambiguous

Warn if a module could be mistakenly parsed as a script by a consumer leveraging Unambiguous JavaScript Grammar to determine correct parsing goal.

Will respect the parserOptions.sourceType from ESLint config, i.e. files parsed as script per that setting will not be reported.

This plugin uses Unambiguous JavaScript Grammar internally to decide whether dependencies should be parsed as modules and searched for exports matching the imported names, so it may be beneficial to keep this rule on even if your application will run in an explicit module-only environment.

Rule Details

For files parsed as module by ESLint, the following are valid:

import 'foo'
function x() { return 42 }

export function x() { return 42 }

(function x() { return 42 })()
export {} // simple way to mark side-effects-only file as 'module' without any imports/exports

...whereas the following file would be reported:

(function x() { return 42 })()

When Not To Use It

If your application environment will always know via some other means how to parse, regardless of syntax, you may not need this rule.

Remember, though, that this plugin uses this strategy internally, so if you were to import from a module with no imports or exports, this plugin would not report it as it would not be clear whether it should be considered a script or a module.

Further Reading

• Unambiguous JavaScript Grammar
• parserOptions.sourceType
• node-eps#13