window.setInterval (chsize , 500);

function chsize() {
    width = document.documentElement.clientWidth;
        if (width < 1185) {
            document.getElementById("bike").src = "images/bike-.jpg"
            document.getElementById("content_photo").style.display = "none";
        }
        else {
            document.getElementById("bike").src = "images/bike+.jpg"
            document.getElementById("content_photo").style.display = "block";
        }
}