3 missing JS functions

vanilla.js

let $ = (sel, el) => typeof sel === "string" ? (el || document).querySelector(sel) : sel || null,
    $$ = (sel, el) => Array.prototype.slice.call((el || document).querySelectorAll(sel));

function on(sel, handlers) {
    $$(sel).forEach(e => {
        Object.keys(handlers).forEach(function (evt) {
            let fn = handlers[evt];
            if (typeof evt === 'string' && typeof fn === 'function') {
                e.addEventListener(evt, fn.bind(e));
            }
        })
    });
}

/* Usage Examples: */

$("#preview").innerHTML = "...";

$$(`a[href="${hash}"]`).forEach(el => el.classList.add('active'));

on('.hero .tab', {
    click: function(evt) { this.classList.toggle('active') }
})
on('form input', {
    keyup: function(evt) { }
})
on('.menu select', {
    change: function(evt) { }
})