That solution doesn't cast javascript in a positive light.

Why should you need to know that much about the guts of the language just to create an associative array that works properly?

JavaScript objects aren't associative arrays. They inherit property values from their prototype. Not just __proto__, but hasOwnProperty, etc. If you want to abuse objects in this way, it makes sense that you need a special approach to opt out of inheritance.

A better approach is to just use Map.

var m = new Map();

It would have been so much better if inheritance was opt-in rather than opt-out.