TypeScript won't import index.js when index.d.ts is present - node.js

Question

I'm having strange behavior in TypeScript right now. In a folder separate from my source folder I have generated JS (protobufjs) with type definitions. When I try to import the index file from that folder I get the error [foldername]/index.d.ts is not a module. This even happens if I explicitly import [folder]/index or even [folder]/index.js.
Any idea what could be causing this?
tsconfig looks like this:
{
"compilerOptions": {
"target": "es2017", /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019' or 'ESNEXT'. */
"module": "commonjs",
"declaration": true, /* Generates corresponding '.d.ts' file. */
"declarationMap": true, /* Generates a sourcemap for each corresponding '.d.ts' file. */
"sourceMap": true, /* Generates corresponding '.map' file. */
"outDir": "./dist", /* Redirect output structure to the directory. */
"rootDir": "./src", /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
"composite": true, /* Enable project compilation */information */
"removeComments": true, /* Do not emit comments to output. */
"strict": true, /* Enable all strict type-checking options. */
"noImplicitAny": true, /* Raise error on expressions and declarations with an implied 'any' type. */
"strictNullChecks": true, /* Enable strict null checks. */
"strictFunctionTypes": true, /* Enable strict checking of function types. */
"strictBindCallApply": true, /* Enable strict 'bind', 'call', and 'apply' methods on functions. */
"strictPropertyInitialization": true, /* Enable strict checking of property initialization in classes. */
"noImplicitThis": true, /* Raise error on 'this' expressions with an implied 'any' type. */
"alwaysStrict": true, /* Parse in strict mode and emit "use strict" for each source file. */
"noUnusedLocals": true, /* Report errors on unused locals. */
"noUnusedParameters": true, /* Report errors on unused parameters. */
"noImplicitReturns": true, /* Report error when not all code paths in function return a value. */
"noFallthroughCasesInSwitch": true, /* Report errors for fallthrough cases in switch statement. */
"esModuleInterop": true /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
},
"include": [ "src" ],
"exclude": [ "test" ]
}
And possibly of note, the generated file I'm importing is under proto, in the same parent folder as src, and imported via e.g. import * as protos from "../../proto";.
I'm also fairly certain this worked until recently, so some configuration might have changed or a module version updated that I haven't caught as this is a team project. Node 13.9.0, TypeScript 3.7.2.

Answer 1

I just tested this... this is my folder structure
_[project root]
|_test
|_test.js
|_index.d.ts
|_index.ts
|_tsconfig.json
|_package.json
|_package.lock.json
The trick was adding the path to [project root]/test/index.d.ts to my tsconfig.json file.. After that, I no longer got the error about "not a module".. I am assuming your index.d.ts has the declare module statement in it...
// tsconfig.json
{
"compilerOptions": {
"target": "ESNEXT",
"module": "commonjs",
"outDir": "./dist",
"strict": true,
"esModuleInterop": true,
"forceConsistentCasingInFileNames": true
},
"include": [
// THIS IS WHAT FIXED IT
"test/index.d.ts"
]
}
// /test/index.d.ts
declare module 'test'
// /test/test.js
function test() {
console.log('test');
}
// Not sure if you're using `module.exports` or not
export default test;
// index.ts
import test from './test/test';
test()