ES6语法中的这些（）是什么？

Question

I see this code:

const enhance = withHandlers({
    signIn: ({ signIn, provider }) => () => signIn(provider)
});

I understand enhance is a function. signIn is also a function, but what's the meaning of the empty () in between? Why can't it just be:

signIn: ({signIn, provider}) => signIn(provider)

Answer 1

No. The () is part of the arrow function. It's a function that returns a function. Let me break it down:

signIn: ({ signIn, provider }) => () => signIn(provider)
        ^                      ^   ^
     Destructuring        Implicit No argument
     assignment           return   arrow function
     for arguments

The property signIn is a method that takes in an object argument and returns a function which executes signIn(provider) .

Your version:

signIn: ({signIn, provider}) => signIn(provider)

Does not return a function that executes signIn(provider) , it returns the return value of signIn(provider) .