javascriptundefinedvoid

JavaScript `undefined` vs `void 0`

What exactly is the difference between undefined and void 0 ?

Which is preferred and why?

Solution

  • The difference is that some browsers allow you to overwrite the value of undefined. However, void anything always returns real undefined.

    (function (undefined) {

undefined = 1;
console.log(typeof undefined);   // "number"
console.log(typeof void 0);      // "undefined"

})();