Can I extend the undefined object like any other object?

Question

I want to create a method for the String object that checks if it\'s undefined:

String.prototype.isDefined = (str) => typeof str === \'undefined\         


        

Answer 1

No, you can't. undefined is not an object, it's a value.

You can't possibly write a function that checks if a string is undefined. If it's undefined, it's not a string. It's undefined.

I don't see what is not clean or readable with

function isDefined(x) { return x !== undefined; }