James B James B - 2 months ago 54
Javascript Question

Typescript Duplicate Function Implementation

I have defined the following two function signatures in the same Typescript class, i.e.,

public emit<T1>(event: string, arg1: T1): void {}


and

public emit<T1,T2>(event: string, arg1: T1, arg2: T2): void {}


However when transpiling the typescript I get the following error

error TS2393: Duplicate function implementation.


I thought you could overload functions in typescript providing the number of parameters in the function signature were different. Given that the above signatures have 2 and 3 parameters respectively, why am I getting this transpilation error?

Answer

I'm assuming your code looks like this:

public emit<T1>(event: string, arg1: T1): void {}
public emit<T1,T2>(event: string, arg1: T1, arg2: T2): void {}
public emit(event: string, ...args: any[]): void {
    // actual implementation here
}

The problem is that you have {} after the first 2 lines. This actually defines an empty implementation of a function, i.e. something like:

function empty() {}

You only want to define a type for the function, not an implementation. So replace the empty blocks with just a semi-colon:

public emit<T1>(event: string, arg1: T1): void;
public emit<T1,T2>(event: string, arg1: T1, arg2: T2): void;
public emit(event: string, ...args: any[]): void {
    // actual implementation here
}