Run a function if a media query matches or once the media query eventually matches

lazy.js

var lazy = function (mediaQuery, load, unload) {
    'use strict';
    
    if (typeof mediaQuery !== 'string') return;
    if (typeof load !== 'function') return;

    var mql = matchMedia(mediaQuery);
    var isLoaded = false;

    if (mql.matches) {
        load();
        isLoaded = true;
        
        if (typeof unload !== 'function') return;
    }

    mql.addListener(function () {
        if (mql.matches && !isLoaded) {
            load();
            isLoaded = true;
        } else if (typeof unload === 'function' && !mql.matches && isLoaded) {
            unload();
            isLoaded = false;
        }
    });
};