JSFiddle - React, Tailwind, and code Playground

JavaScript

var obj = {a: null, x:1,y:'str',z:{a:1,b:2}};
console.log(JSON.stringify(obj));
console.log(JSON.stringify(obj,["x","y","z"]));
console.log(JSON.stringify(obj,["x","y","z", "a", "b"]));