Why does adding function as in A3 or removing function as in B3 cause errors?

Question

Why does adding function as in A3 or removing function as in B3 cause errors?

Version A1

let x = {
    func: function () {
        console.log(`Hi`);
    }
}

Version A2

let x = {
    func() {
        console.log(`Hi`);
    }
}

Version A3 (Not Working)

let x = {
    function func() {
        console.log(`Hi`);
   }
}

Version B1

let func = function () {
    console.log(`Hi`);
}

Version B2

function func() {
    console.log(`Hi`);
}

Version B3 (Not Working)

func() {
    console.log(`Hi`);
}

Answer 1

The reason is that the syntax and grammar defined for JavaScript does not provide for the validity of the code you have written.

Simply put, the code is invalid.