What is the exact meaning of Git Bash.

Using setTimout to execute a function written in arrow syntax gives me an error

Begay

When I execute this code I receive an error: Cannot access 'bye' before initialization

setTimeout(bye, 3000);

console.log('Hello');

let bye = () => console.log('Goodbye');

But if I change the function to regular function syntax, it executes as I would expect it to. Why is this happening, and is there a way to make this work with arrow syntax?