eval() has no legit use case in JS, and I really don't understand what the point of "// @export" would be. You can't reflect on module or function scopes, but that's a feature and gives you encapsulation.
for-in is a legacy feature; due to dynamic inheritance, it's generally not safe to use without also calling Object#hasOwnProperty() every iteration. for-of is not for "array elems", it uses the iteration protocols that are implemented for all built-in collection types, not just Array, and some DOM types, and can be implemented for any user types. Protocols are a much more flexible and clean approach to metaprogramming than overloading the for-in looping construct would be.
You can't use Proxy if you need to target legacy browsers like IE9, and Vue needs to, since it's about 15% of all browsers.
for-in is a legacy feature; due to dynamic inheritance, it's generally not safe to use without also calling Object#hasOwnProperty() every iteration. for-of is not for "array elems", it uses the iteration protocols that are implemented for all built-in collection types, not just Array, and some DOM types, and can be implemented for any user types. Protocols are a much more flexible and clean approach to metaprogramming than overloading the for-in looping construct would be.
You can't use Proxy if you need to target legacy browsers like IE9, and Vue needs to, since it's about 15% of all browsers.