switch 語(yǔ)句用于基于不同的條件來(lái)執(zhí)行不同的動(dòng)作。
JavaScript Switch 語(yǔ)句
請(qǐng)使用 switch 語(yǔ)句來(lái)選擇要執(zhí)行的多個(gè)代碼塊之一。
語(yǔ)法
switch(n) { case 1: 執(zhí)行代碼塊 1 break; case 2: 執(zhí)行代碼塊 2 break; default: n 與 case 1 和 case 2 不同時(shí)執(zhí)行的代碼 } 工作原理：首先設(shè)置表達(dá)式 n（通常是一個(gè)變量）。隨后表達(dá)式的值會(huì)與結(jié)構(gòu)中的每個(gè) case 的值做比較。如果存在匹配，則與該 case 關(guān)聯(lián)的代碼塊會(huì)被執(zhí)行。請(qǐng)使用 break 來(lái)阻止代碼自動(dòng)地向下一個(gè) case 運(yùn)行。
實(shí)例
顯示今日的周名稱。請(qǐng)注意 Sunday=0, Monday=1, Tuesday=2, 等等：
var day=new Date().getDay(); switch (day) { case 0: x="Today it's Sunday"; break; case 1: x="Today it's Monday"; break; case 2: x="Today it's Tuesday"; break; case 3: x="Today it's Wednesday"; break; case 4: x="Today it's Thursday"; break; case 5: x="Today it's Friday"; break; case 6: x="Today it's Saturday"; break; } x 的結(jié)果：
Today it's Wednesday
親自試一試
<!DOCTYPE html>
<html>
<body>
<p>點(diǎn)擊下面的按鈕來(lái)顯示今天是周幾：</p>
<button onclick="myFunction()">點(diǎn)擊這里</button>
<p id="demo">時(shí)間</p>
<script>
function myFunction()
{
var x;
var d=new Date().getDay();
switch (d)
{
case 0:
x="Today it's Sunday";
break;
case 1:
x="Today it's Monday";
break;
case 2:
x="Today it's Tuesday";
break;
case 3:
x="Today it's Wednesday";
break;
case 4:
x="Today it's Thursday";
break;
case 5:
x="Today it's Friday";
break;
case 6:
x="Today it's Saturday";
break;
}
document.getElementById("demo").innerHTML=x;
}
</script>
</body>
</html>
default 關(guān)鍵詞
請(qǐng)使用 default 關(guān)鍵詞來(lái)規(guī)定匹配不存在時(shí)做的事情：
實(shí)例
如果今天不是周六或周日，則會(huì)輸出默認(rèn)的消息：
var day=new Date().getDay(); switch (day) { case 6: x="Today it's Saturday"; break; case 0: x="Today it's Sunday"; break; default: x="Looking forward to the Weekend"; } x 的結(jié)果：
Looking forward to the Weekend
親自試一試