JAVASCRIPT

js - change div height on scroll

var header = document.getElementById("header_parent");

window.onscroll = function(e) {
    if(window.scrollY) {
        if(window.pageYOffset > 50) {
            header.style.height = 30;
        } else {
            header.style.height = 50;
        }
    }
}

change height of div with scroll in javascript

$(window).on('scroll', function () {
    var scrollTop = $(window).scrollTop();
    if (scrollTop > 50) {
        $('#header_parent').stop().animate({height: "30px"},200);
    }
    else {
         $('#header_parent').stop().animate({height: "50px"},200);   
    }
});