JSFiddle - React, Tailwind, and code Playground
JavaScript
let a = 'abc', b;
let undef = {
a: a,
b: b
}
document.write('v1, define undefined property:' + JSON.stringify(undef) + '<br>');
console.log(undef);
undef.a = undefined;
document.write('v2, redefine defined property to undefined:' + JSON.stringify(undef));
console.log(undef);