iterator by object

/**
 * @example for (let {key, val} of listeners) { console.log("2", key, val); }
 */
const listeners = {};
listeners[Symbol.iterator] = function () {
    const keys = Object.keys(this);
    const self = this;
    var current = 0;
    var last = keys.length;

    return {
        next() {
            if (current < last) {
                return {
                    done: false,
                    value: {
                        key: keys[current],
                        val: self[keys[current++]]
                    }
                }
            }
            return {
                done: true
            }
        }
    }
};