[esprehn]

That's not magic, it's just how property getter and setters work on the global:

    <script>
        var _value = "test value";
        Object.defineProperty(window, "testName", {
            get: () => _value,
            set: (value) => { _value = String(value) },
        });
    </script>
    <script>
        var testName = {};
        // prints [object Object] string
        console.log(testName, typeof testName);
        var name = {};
        // prints [object Object] string
        console.log(name, typeof name);
    </script>

the `var` doesn't create a new property since the getter and setter already exist.

Other properties have the same behavior, for example `status`.

Note: there's also LegacyUnforgeable which has similar behavior: https://webidl.spec.whatwg.org/#LegacyUnforgeable

Even if you're not using modules, using an IIFE avoids all this by making your variables local instead of having them define/update properties on the global.