let x = 0; function typeof_wrapper(y) { return typeof y; } (function() { typeof_wrapper(x); // throws an error let x = 1; })();

let x = 0; function typeof_wrapper(y) { return typeof y; } (function() { typeof_wrapper(x); // throws an error let x = 1; })(); (function() { typeof_wrapper(x); // returns "undefined" var x = 1; })(); Again, typeof isn't throwing the error, the runtime is, because a variable declared with "let" is being referenced before the declaration. It's not inconsistent, it's one of the main points of "let". You're essentially arguing that a feature added because the old behaviour was undesirable is inconsistent because it's not exhibiting the old undesirable behaviour.