webidl/ecmascript-binding/attributes-accessors-unique-function-objects.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>All attributes accessors are unique function objects</title>
<link rel="help" href="https://webidl.spec.whatwg.org/#idl-interface-mixins">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
"use strict";

test(() => {
  const seenPrototypes = new WeakSet([Function.prototype]);
  const seenFunctions = new WeakMap();

  for (const windowKey of Object.getOwnPropertyNames(window)) {
    const windowValue = window[windowKey];
    if (typeof windowValue !== "function") continue;

    const {prototype} = windowValue;
    if (!prototype || seenPrototypes.has(prototype)) continue;
    seenPrototypes.add(prototype);

    for (const key of Object.getOwnPropertyNames(prototype)) {
      const assert_not_seen = (fn, field) => {
        const fnInfo = `${windowKey}.${key}.${field}`;
        assert_equals(seenFunctions.get(fn), undefined, fnInfo);
        seenFunctions.set(fn, fnInfo);
      };

      const desc = Object.getOwnPropertyDescriptor(prototype, key);
      if (desc.get) assert_not_seen(desc.get, "[[Get]]");
      if (desc.set) assert_not_seen(desc.set, "[[Set]]");
    }
  }
}, "For attributes, each copy of the accessor property has distinct built-in function objects for its getters and setters.");
</script>