I'm getting started with TypeScript and at moment I'm following the TypeScript in 5 minutes guide. I'm receiving a strange warning in Visual Studio Code when I hover the mouse over the greeter function name, as shown in the below image. The alert is:

[ts] Duplicate function implementation.

function greeter(person: Person): string (+1 overload)

But there is no other implementation of this unique function in my single file! When I run tsc greeter.ts all works fine and the js file is generated.

The complete greeter.ts file:

interface Person {

    firstName: string;

    lastName: string;

}



function greeter(person: Person) {

    return Hello,  + person.firstName +   + person.lastName;

}



var user = { firstName: Jane, lastName: User };



console.log(greeter(user));

Why am I receiving this alert? How to solve it? I took a look in this question, but I believe it isn't related.