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                        /JavaScript進階篇

switch語句

錯誤代碼：
<!DOCTYPE?HTML>
<html>
<head>
<meta?http-equiv="Content-Type"?content="text/html;?charset=utf-8"?/>
<title>switch</title>
<script?type="text/JavaScript">
?function?b()
?{
?????var?myweek=prompt("今天星期幾？","1");
?????switch(myweek)
?????{
?????????case?1:
?????????case?2:
?????????document.write("學習理論知識");
?????????break;
?????????case?3:
?????????case?4:
?????????document.write("到企業去實踐");
?????????break;
?????????case?5:
?????????document.write("總結經驗");
?????????break;
?????????case?6:
?????????case?7:
?????????document.write("休息娛樂");
?????????break;
?????????default:alert("不查就不查");
?????}
?}
</script>
</head>
<body>
?<input?name="button"?type="submit"?value="查看今日任務"?onclick="b()"?/>
</body>
</html>
正確代碼：
<!DOCTYPE?HTML>
<html>
<head>
<meta?http-equiv="Content-Type"?content="text/html;?charset=utf-8"?/>
<title>switch</title>
<script?type="text/JavaScript">
?function?b()
?{
?????var?myweek=prompt("今天星期幾？","1");
?????switch(myweek)
?????{
?????????case?'1':
?????????case?'2':
?????????document.write("學習理論知識");
?????????break;
?????????case?'3':
?????????case?'4':
?????????document.write("到企業去實踐");
?????????break;
?????????case?'5':
?????????document.write("總結經驗");
?????????break;
?????????case?'6':
?????????case?'7':
?????????document.write("休息娛樂");
?????????break;
?????????default:alert("不查就不查");
?????}
?}
</script>
</head>
<body>
?<input?name="button"?type="submit"?value="查看今日任務"?onclick="b()"?/>
</body>
</html>


下面代碼就是比上面代碼case值那里多了單引號的區別，請問case值那里什么時候要單引號什么時候不要？why？