We can't delete a local variable that has been declared with var/let/const.

We can only delete properties of objects. This also includes global variables which are implicit properties of the window object. As per the MDN --

The JavaScript delete operator removes a property from an object

If we change the code to the following then delete will work.

window.person = "Yomesh";

var deletePerson = () => {
  delete window.person;
  return window.person;

console.log(deletePerson()); // undefined

To read more -- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/delete

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