1.流程控制语句

条件判断语句：if...else
条件分支语句：switch..case
循环语句：for while do...while

0.1条件判断语句

<style type="text/css">
    .box{
        width: 300px;
        height: 300px;
        background-color: palevioletred;
    }
</style>

<script type="text/javascript">
    window.onload = function () {
        var btn = document.getElementById("btn");
        var box = document.getElementById("box");
        btn.onclick = function () {
            if(box.style.display == "none"){
                box.style.display = "block";
            }else {
                box.style.display = "none";
            }
        }
    }
</script>
</head>
<body>
    <input type="button" value="切换" id="btn">
    <br/>
    <div class="box" id="box"></div>
</body>

0.2多重条件判断语句

switch case如果不使用break会穿透也就是依次往下执行

<script type="text/javascript">
    var today = 4;
    /*if(today == 1){
        alert("语文");
    }else if(today == 2){
        alter("数学");
    }else if (today == 3){
        alert("英语");
    }else  if(today == 4){
        alert("美术");
    }else if(today == 5){
        alert("舞蹈");
    }else {
        alert("不补习");
    }*/

     switch (today) {
         case 1:
             alert("语文");
             break;
         case 2:
             alert("数学")
             break;
         case 3:
             alert("英语")
             break;
         case 4:
             alert("美术")
             break;
         case 5:
             alert("舞蹈")
             break;
         default:
             alert("不补习")
     }
</script>