JSFiddle - React, Tailwind, and code Playground

JavaScript

var var2 = {
    proper: 'a'
};

function fun2(var2) {
     var2.proper = 'b';
     console.log(var2.proper);
   
     var var3 = var2;

     console.log(var3.proper);
}

fun2(var2);

console.log(var2.proper);

console.log(var3.proper);