var mobile = window.matchMedia("(max-width: 768px)"); var $home_hero = $('#home_hero'); var $hero_mobile = $('.hero-mobile') function setHomeHeight() { if (mobile.matches) { vh = window.innerHeight $home_hero.height(vh) $hero_mobile.height(vh) console.log('height has been set') } else { $hero_mobile.css({'height': ''}) console.log('height has been UNset') } } $(document).ready(function() { setHomeHeight() })