I am just curious if there are any difference between using var/let/const to declare arrow function or declare arrow function with out let/var/const.

For example:

hello =()=>{
        console.log('hello')
    }
hello()

let hola = () =>{
        console.log('hola')
    }
   hola()

It seems that that I doesn't use let/const/var won't produce undefined error and no difference, but I saw all the reference resources like MDN and W3school prefer to use let/var/const to declare them?

Is there any performance difference between them and will it cause error if I doesn't use let/var/const to define it?

Thanks for any responds!