Untitled

<style>
    body.mobile .no-mobile { display: none; }
</style>
<body>
    ...
    <div class="no-mobile">
       ...
    </div>
    ...
    <script>
        if(window.innerWidth < 800) {
            var body = (document.getElementByTagName("body"))[0];
            body.className = "mobile";
        }
    </script>
</body>

<script>
    if(window.innerWidth < 800)
    {
        var divS = new Array("id_2", "id_4");
        alert("div'ы " + divS + " не показываются");
    }
</script>

<div id="id_1">ID 1</div>
<div id="id_2">ID 2</div>
<div id="id_3">ID 3</div>
<div id="id_4">ID 4</div>
<div id="id_5">ID 5</div>