immutable javascript

let string1 = "string pertama";
let string2 = string1;
console.log(tring2); //string pertama
string2 = "string berubah";
console.log(string1);// string pertama
console.log(string2);//string berubah

let angka1 = 1;
let angka2 = angka1;
angka2 = 3;
console.log(angka1);//1
console.log(angka2);//3