Inaccessible Local Variables

Effect

Some variables declared may be inaccessible, and references using those as RHS may see a value even if the variable has never been assigned.

Background

The label arguments in a function is not assignable on most browsers. The label in a catch block may or may not be accessible outside that block depending on browser, and may mask local variables declared in the enclosing function.

Assumptions

Untrusted code can declare local variables with these names, and static checkers forgo restrictions based on whether a variable has been assigned a value.

Versions

Differs

Example

(function () {
   var arguments;
   alert('arguments === undefined: ' + (arguments === undefined));
 })();

(function () {
   var e;
   try {
     throw 1;
   } catch (e) {
   }
   alert('arguments === undefined: ' + (arguments === undefined));
 })();

(function () {
   var e = 1;
   try {
     throw 2;
   } catch (e) {
   }
   alert('e === 1 : ' + e);
 })();