Better dead code elimination

no-unreachable fails to detect some of the cases of unreachable code. For example,

(function() {
  var foo = null;
  if (!foo) {
    return;
  } 
  (function dead(){})();
})();

should warn about dead function (since it’s statically determinable).

[ilyavolodin]

If we were to add something like this to ESLint, I would seriously consider adding it to Escope instead. Escope already checked all of the declarations in the AST, so enhancing it to track type inference would be simpler then adding something like that to ESLint core itself.

[sebmck]

We’re working on some Babel tooling that uses it’s APIs. Babel scope tracking tracks constant values and knows that foo will always be null. Then some of our evaluation helpers determine that if (!foo) will always be true. There’s no Flow type information required.