JavaScript library declaration files are essential for providing type definitions and enabling

I have encountered a problem with my JS library and its declaration files (*.d.ts) in my TypeScript projects. For some reason, my TS project seems to be ignoring these declaration files.


To investigate this issue further, I decided to conduct a simple test within my TS project.

// project/src/calculateSum.js

function calculateSum(a, b) {
  return a + b
}

module.exports = {
  calculateSum
}
// project/src/types/custom/calculateSum.d.ts

export declare function calculateSum(a: number, b: number): number;
// project/src/app.ts

import { calculateSum } from './calculateSum`

console.log(calculateSum('it should not acceept string', 1))

Surprisingly, neither VS code nor TS reported any issues with the code above.

Below is a snippet of my tsconfig.json:

{
  "compilerOptions": {
    ...
    "skipLibCheck": true,
      "typeRoots": [
        "node_modules/@types",
        "src/types/custom"
      ]
  },
  "include": [
    "./src/**/*",
  ],
    "exclude": [
      "node_modules"
    ]
}

In addition, I also have an svg.d.ts file within src/types/custom, and surprisingly, it works as expected.

// project/src/types/custom/svg.d.ts
declare module "*.svg" {
    import React = require("react")
    export const AsComponent: React.FC<React.SVGProps<SVGSVGElement>>
    const src: string
    export default src
}

It appears that there might be something I am misunderstanding in this scenario.

Answer №1

From what I understand, it is important for the type definitions of your .js files to be located in the same directory in order for them to function properly. This is because there can be multiple definition files containing the same function declaration.

Your svg.d.ts file seems to be working as intended, likely due to it being a general definition for all *.svg imports (I believe).

You may also want to refer to this response on a related issue:

Answer №2

To implement this solution, update your tsconfig.json file with the following:

"compilerOptions": {
  ...
  "rootDirs": ["src", "src/types/custom"],
  ...
}

More information on TS documentation

By using rootDirs, you can indicate to the compiler that there are multiple "virtual" directories functioning as a single root. This enables the compiler to resolve relative module imports within these "virtual" directories, treating them as if they were combined into one directory.

Additionally, it is advisable to remove the entire "typeRoots" field from your tsconfig.json: this should no longer be necessary.

Keep in mind: you may also require "allowJs": true, otherwise the tsc compiler will not generate your .js files.

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