Loading纯JS

function showLoading() {
        document.getElementById("over").style.display = "block";
        document.getElementById("layout").style.display = "block";
    }
 function removeLoading() {
        document.getElementById("over").style.display = "none";
        document.getElementById("layout").style.display = "none";
}

.over {
            display: none;
            position: absolute;
            top:;
            left:;
            width: 100%;
            height: 100%;
            background-color: #f5f5f5;
            opacity: 0.5;
            z-index:;
        }

.layout {
            display: none;
            position: absolute;
            top: 40%;
            left: 40%;
            width: 20%;
            height: 20%;
            z-index:;
            text-align: center;
        }

<div id="over" class="over"></div>
<div id="layout" class="layout"><img src="../../images/loading.gif" alt=""/></div>