prototypes.js

function findEnumerableProperties(obj) {
    let enumerableProperties = []
    let descriptors = Object.getOwnPropertyDescriptors(obj)
    for (let k in descriptors)
        if (descriptors[k].enumerable) 
            enumerableProperties.push(k)
    return enumerableProperties
}

let builtins = [Object, Array, String, Number, Boolean, RegExp, Set, Map, Date, WeakMap, WeakSet, WeakRef, Function, Event, Element]
for (let ctor of builtins)
    console.log(
        ctor.name, 
        'prototype has', 
        findEnumerableProperties(ctor.prototype).length, 
        'enumerable properties'
    )