undefined is not mutable in ECMAScript 5

[specious]

No description provided.

[omninonsense]

This isn't exactly true. If we're talking about undefined as a reference, it is still only an immutable (unwritable, & unconfigurable) property of the global object (hence, a global reference).

However, you cold still redefine what value undefined references in a different scope. Meaning, that the following code is valid (but silly) JavaScript:

(function (global) {
  var undefined = 10;
  return (undefined * 4 + 2);
})(this); // returns 42

[specious]

Superseded by #164.