Breaking Proxy?

[Jack-Works]

Proxy is designed to be non-distinguishable from normal objects. If structs are typeof === "object", then the Proxy of structs can be detected with the following code.

function isProxyOfStruct(x) {
    try {
        struct class extends x {}
        return true
    } catch {
        return false // Nah, it's a proxy
    }
}

[ljharb]

You can already easily determine if anything is a proxy of any specific builtin, except Error, Function, and Array.

[syg]

Doesn't that example also return false for regular objects?

[Jack-Works]

Doesn't that example also return false for regular objects?

Yes, I mean the "Proxy of structs".

I agree this isn't a problem because of all those Web APIs that reads internal slots directly.

[ljharb]

Not just web; every 262 builtin (besides Error) reads internal slots, and only Function and Array effectively tunnel through proxies.