I noticed that this throws in both Chrome and Firefox:

const k = [1,2,3];
const p = new Proxy(k, {});
indexedDB.cmp(k, p);

In Chrome, at least, the proxy fails an internal "is this an array?" check.

In the spec convert a value to a key calls ECMAScript's IsArray which would seem to return true for array proxies.

At the very least, we don't have tests.

Should we update the spec to exclude proxies, e.g. replacing "if IsArray(input)" with "if input is an Array exotic object"?

Alternately, should array proxies be supported? What are the consequences of allowing these? Would the value→key conversion algorithm potentially blow up in more places?