Check if JS object is a proxy

isProxy.js

// Credit to https://stackoverflow.com/a/49651719 and https://stackoverflow.com/a/60323358

const isProxy = obj => {
    try {
        postMessage(obj, window);
    } catch (error) {
        return error && error.code === 25;
    }
    
    return false;
};

This could be shortened to use structuredClone. However, in adversarial context this is invasive, since the object knows it's being checked (some handlers might be executed before an exception is thrown)