TS7010

error TS7010: ‘sum‘, which lacks return-type annotation, implicitly has an ‘any‘ return type.

Broken Code ❌

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namespace MyModule {
  export function sum(a: number, b: number);
}

Fixed Code ✔️

You have to add a return-type annotation and preferably a function implementation:

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namespace MyModule {
  export function sum(a: number, b: number): number {
    return a + b;
  }
}