1. if分支

if(條件1){
      ...
}else if(條件2){
      ...
}else{
}

##      2. switch
```#js
switch(expression){
      case value:
            statement;
            break;
      case value:
            statement;
            break;
      default:
            statement;
}

<script type="text/javascript">
	var week = new Date().getDay();
	var weekstr;
	switch(week){
		case 0:
			weekstr="日";
			break;
		case 1:
			weekstr="一";
			break;
		case 2:
			weekstr="二";
			break;
		case 3:
			weekstr="三";
			break;
		case 4:
			weekstr="四";
			break;
		case 5:
			weekstr="五";
			break;
		case 6:
			weekstr="六";
			break;
		default:
			weekstr="...系統錯誤，你是怎麼走到這一步的";
			break;
	}
	document.write("今天是星期"+weekstr);
</script>
 

3.for迴圈

for(var i=0;i<100;i++){
      console.log(i);
}

4.while迴圈

先判斷，後執行：while(){}
先執行，後判斷：do{}while()

<script type="text/javascript">
var i=0;
while(i<10){
	console.log(i);
	i++;
}
var j=0;
do{
    console.log(j);
    j++;
}while(j<5)
</script>

5. break和continue

break：立即退出迴圈
continue：結束本次迴圈，繼續開始下一次