JSFiddle - React, Tailwind, and code Playground

JavaScript

var symbol = Symbol();
var object = {};

Object.defineProperty(object, symbol, {
  value: 'value',
  enumerable: true
});

Object.defineProperty(object, 'foo', {
  value: 'bar',
  enumerable: true
});

Object.defineProperty(object, 'boo', {
  value: 'baz',
  enumerable: false
});

Object.defineProperty(object, () => {}, {
  value: 'bin',
  enumerable: true
});

document.write('for in:<br>');
for (let f in object) {
  document.write(f, ' = ', object[f]);  document.write('<br>');
}
document.write('<br>for of:<br>');
for (let k of Object.getOwnPropertyNames(object)) {
  document.write(k);   document.write('<br>');
}