获取浏览器宽高（涵盖所有浏览器）

<p id="demo"></p>

<script>
    var w = window.innerWidth
        || document.documentElement.clientWidth
        || document.body.clientWidth;
    var h = window.innerHeight
        || document.documentElement.clientHeight
        || document.body.clientHeight;
    x = document.getElementById("demo");
    x.innerHTML = "浏览器window宽度: " + w + ", 高度: " + h + "。"
    document.write("可用宽度: " + screen.availWidth);
    document.write("可用高度: " + screen.availHeight);
</script>