JSFiddle - React, Tailwind, and code Playground

JavaScript

function Foo()
{
   this.a = 3;
   this.b = 2;
   this.test = function() {return this.a*this.b;};
}


var fooObj = new Foo();
alert(fooObj.test() ); //Prints 6
var fooJSON = JSON.parse(`{"a":4, "b": 3}`, function(key,value){
if(key!=="") return value; //logic of cause should be more complex for handling nested objects etc.
  let res = new Foo();
  res.a = value.a;
  res.b = value.b;
  return res;
});
//Something to convert fooJSON into a Foo Object
//....... (this is what I am missing)
alert(fooJSON.test() ); //Prints 12