Introduction

In TypeScript, the "Duplicate function implementation" error appears when a function is defined more than once in the same scope.

To avoid undesired behavior that can result from having two distinct implementations of the same method, this error is raised.

Having Unique Function Names

The most frequent reason for this issue is when two separate files or modules include functions with the same name.

Here is an illustration of how this mistake may happen:

test1.ts:

const multiply_number = (x: number, y: number): number => {
return x * y
}

test2.ts:

const multiply_number = (a: number, b: number): number => {
return a * b
}

The function multiply_number is defined in two distinct files in the code above. The following error message appears when we try to build this code:

Duplicate function implementation.

This error can be solved in two ways;

1. Make sure the names of each function are unique.

2. If two files must have the same function name (which isn't advisable) then you can add export {} to the end of each file.

Calling A Function Where It Defined

This error message can also occur when you call a function where it was defined. The code below will explain more about this.

data.ts:

interface People {
    name: string
}

function Person(str: People) {
    console.log(str.name)
}

Person({name: 'Oluwaseyi'})

The code above runs in the console, but still logs out the error message

Duplicate function implementation.

To fix this, all we need to do is to add export {} at the end of the file like so:

interface People {
    name: string
}

function Person(str: People){
    console.log(str.name)
}

Person({name: 'Oluwaseyi'})

export {}

When naming functions and modules in TypeScript, it's vital to adhere to best practices, such as providing names that are distinctive and descriptive.

It will be simpler to manage your code and less likely that duplication will occur as a result.

Conclusion

As a result, when a function is defined more than once in the same scope, TypeScript throws the "Duplicate function implementation" error.

You can either remove one of the implementations or rename the functions to fix the problem.

You can also fix this by adding export {} to the end of each file.

You may prevent this mistake from happening again by adhering to standard practices for naming functions and modules.