There are two uses for this rule:

1. to enforce file extensions are always used,

2. to enforce file extensions are never used.

If you want to enforce file extensions are always used and you're **NOT** using `moduleResolution` `node16` or `nodenext`, then there's not really a good alternative for you, and you should continue using the `import/extensions` lint rule.

If you want to enforce file extensions are always used and you **ARE** using `moduleResolution` `node16` or `nodenext`, then you don't need to use the lint rule at all because TypeScript will automatically enforce that you include extensions (TS 2834 & 2835)!

On the surface `import/extensions` seems like it should be fast for this use case, however the rule isn't just a pure AST-check - it has to resolve modules on disk so that it doesn't false positive on cases where you are importing modules with an extension as part of their name (eg `foo.js` resolves to `node_modules/foo.js/index.js`, so the `.js` is required). This disk lookup is costly and thus makes the rule slow.

If your project doesn't use any `npm` packages with a file extension in their name, nor do you name your files with two extensions (like `bar.js.ts`), then this extra cost probably isn't worth it, and you can use a much simpler check using the [`no-restricted-syntax`](https://eslint.org/docs/latest/rules/no-restricted-syntax) lint rule.

The below config is several orders of magnitude faster than `import/extensions` as it does not do disk lookups, however it will false-positive on cases like the aforementioned `foo.js` module.

function banImportExtension(extension) {

const message = `Unexpected use of file extension (.${extension}) in import`;

const literalAttributeMatcher = `Literal[value=/\\.${extension}$/]`;

return [

{

// import foo from 'bar.js';

selector: `ImportDeclaration > ${literalAttributeMatcher}.source`,

message,

},

{

// const foo = import('bar.js');

selector: `ImportExpression > ${literalAttributeMatcher}.source`,

message,

},

{

// type Foo = typeof import('bar.js');

selector: `TSImportType > TSLiteralType > ${literalAttributeMatcher}`,

message,

},

{

// const foo = require('foo.js');

selector: `CallExpression[callee.name = "require"] > ${literalAttributeMatcher}.arguments`,

message,

},

];

}

module.exports = {

// ... other config ...

rules: {

'no-restricted-syntax': [

'error',

...banImportExtension('js'),

...banImportExtension('jsx'),

...banImportExtension('ts'),

...banImportExtension('tsx'),

],

},

};