Web APIs are relying more and more on dictionaries. And doing feature detection of such members requires ugly and unnecessary complicated code. Following WICG/EventListenerOptions#31, #491, and many more over the years, I'm proposing WebIDL allows us to expose interfaces under a specific "namespace/scope" to avoid polluting the global scope.

Current state for an API called MyAPI

1. A dictionary makes it unnecessarily hard to detect its members.

dictionary MyDictionaryOptions {
  boolean foo;
};

2. An interface pollutes global scope as window.MyDictionaryOptions now unnecessarily exists.

[Exposed=Window]
interface MyDictionaryOptions {
  boolean foo;
}

Proposal

Use interfaces instead of dictionaries when possible and expose them under a specific member of the API.

[Exposed=Window.MyAPI] // <-- NEW!
interface MyDictionaryOptions {
  boolean foo;
}

if ("foo" in window.MyAPI.MyDictionaryOptions) {
  // 1. It's easy to detect foo exists in MyDictionaryOptions 
  // 2. Detecting it does not pollute global scope
  // 3. It does not require executing some methods to test it.
}

What do you folks think about this?