Is there a method in Typescript to constrain an exported function's accessibility so that it is only importable by specific files?

I would like developers to use a class or interface instead of directly importing functions.

Is there a way to restrict so only the class can import the function?

I prefer not to consolidate all the functions in a single file, especially in a large project where scalability is crucial.

For instance, I am trying to avoid this traditional pattern:

// myclass.ts

// excluding function exports
function foo(){ ... }
function bar(){ ... }

export class MyClass {
 Foo(){ return foo() }
 Bar(){ return bar() }
}

Here is the desired approach:

// foo.ts
export function foo(){ ... } 
// I intend for this to be private while still being exported to be used by the class below

// bar.ts
export function bar() { ... }

// myclass.ts
import { foo } from 'foo';
import { bar } from 'bar';

export class MyClass {
 Foo(){ return foo() }
 Bar(){ return bar() }
}

// anyotherfile.ts
import { foo } from 'foo' // Prevent direct import
import { MyClass } from 'myclass' // Use this method instead

Answer №1

If you are creating an npm package, it's important to consider that not everything in your project is just source code dependencies.

If your situation is different, achieving your desired outcome may be challenging without some magic. Unlike Java, Typescript does not have a concept of 'package level' exports.

Make sure that the entry point to your library or package is set to index.js.

For example, if you have the following structure: module/ functions/ MyClass.ts index.ts

//a.ts
export function a(): any // export this from files inside functions/

Then your class will function as intended.

//MyClass.ts
import { a } from './functions/a'
 
export class MyClass {
    a(): any {
         return a()
    }
}

To restrict access to only the class from outside the module, export only the class in the module's index file.

//index.ts
export * from './MyClass'

By doing this, anyone installing your package will only be able to import MyClass from '@yourpackage-name'.

However, they could potentially try to import from '@yourpackage-name/build/src/functions/a' as a workaround.

I hope this explanation is helpful for you.

Answer №2

When working with TypeScript, it is possible to restrict imports in a clever way.

If you are concerned about developers using your classes, especially if you are distributing them as an npm package, you likely have a build step in place.

One approach in your build process is to modify the function declarations in your .d.ts files like this:

export const foo: never

This approach will lead to a TypeScript error if developers attempt to use the functions you are trying to protect.
Of course, developers can bypass this by using // @ts-ignore, but at least they will be aware that they are not utilizing your library as intended.

While adjusting files in the build step can be tricky, an alternative is to exclude the .d.ts files for your "hidden" scripts.
Although developers may not receive an error when importing them, the absence of types should signal to them that they are not interacting with the correct API.


If you want to ensure that developers do not import certain functions, consider bundling all your scripts into one file as part of your build process.

Many npm packages adopt this bundling approach to streamline package size and enhance build efficiency for developers.

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