Difference between browser-supported handlers and Shazzer 'events' list

function listAllEventHandlers() {
    const allHandlers = new Set();
    const objects = [document.body, document, window];
    objects.forEach(obj => {
        for (const prop in obj) {
            if (prop.startsWith('on')) {
                allHandlers.add(prop);
            }
        }
    });
    return Array.from(allHandlers).sort();
}
allBodyHandlers = listAllEventHandlers();

console.log("window, document and document.body contain " + allBodyHandlers .length + " handlers")

const shazzerEvents  = new Set();

shazzerEvents.add('$[data1]');

console.log("Shazzer 'events' contains " + shazzerEvents.size + " events");

function missingHandlers() {
const out = new Set();
    for(let handler of allBodyHandlers) {
        if (!shazzerEvents.has(handler)) {
            out.add(handler);
        }
    }
return out;
}

for(let handler of missingHandlers()){
   log(handler);
}