Why can't I delete javascript values declared with var?

Question

example:

x = "Hello";
delete x; // returns true, x is removed

var y = "Hello";
delete y; // returns false, y is not removed

I'm not interested in How this happens, I want to know why the language has this feature.

Answer 1

Strictly speaking the first x is not a variable but a property of the global object. In browsers it's usually window (so x = "Hello" is equal to window.x = "Hello"). You can't use delete to remove variables but you can use it to remove object properties, and that's what it does in the first case.

Answer 2

This page has a lengthy explanation that spells out the why.

The short answer is delete is for properties, not variables. var y creates a variable. x = "something" creates a property of the global scope.

Also note that not all browsers handle delete the same. cough cough IE