The usage of ES2015 module syntax is favored over custom TypeScript modules and namespaces as per the rule @typescript-eslint/no-namespace. So, it is advised to rewrite the sentence accordingly in any context if necessary.

Fixing the Error in TypeScript

To fix this error, instead of:

export namespace InternalThings {
    export function myFunction() {
    }

    export class MyClass {
    }
}

import { InternalThings } from './internal-things';

InternalThings.myFunction();

you can make all the members of the namespace directly accessible:

export function myFunction() {
}

export class MyClass {
}

Now, you can import it using the following syntax:

import * as InternalThings from './internal-things';

InternalThings.myFunction();

The main advantage of this approach is that users of your module can choose to import only what they need or give your module a custom name:

import * as CustomModuleName from './internal-things';

CustomModuleName.myFunction();

import { MyClass } from './internal-things';

let field = new MyClass();

The error is being reported by eslint. To resolve this issue, you can either exclude the ‘@typescript-eslint/no-namespace’ rule in the eslint configuration or update your code to use ES6 syntax.

The usage of custom TypeScript modules (module foo {}) and namespaces (namespace
foo {}) is considered outdated in organizing TypeScript code. The preferred method now is to use ES2015 module syntax (import/export).

Please refer to the following link for more information: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-namespace.md