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                        /JavaScript進(jìn)階篇

+的運算怎么變成 string型了？

為什么

<!DOCTYPE?html>
<html>

<head>
????<meta?http-equiv="Content-Type"?Content="text/html;?charset=utf-8"?/>
????<title>?事件</title>
????<script?type="text/javascript">
????????function?count(){

????????????//獲取第一個輸入框的值
var?firsttxt=document.getElementById("txt1").value;
????????????//獲取第二個輸入框的值
????????????var?secondtxt=document.getElementById("txt2").value;
????????????//獲取選擇框的值
????????????var?select=document.getElementById("select").value;
????????????//獲取通過下拉框來選擇的值來改變加減乘除的運算法則
var?result;
switch?(select)?{
????case?"+":?result=firsttxt+secondtxt;break;
????case?"-":?result=firsttxt-secondtxt;break;
????case?"*":?result=firsttxt*secondtxt;break;
????case?"/":?result=firsttxt/secondtxt;break;

}
????????????//設(shè)置結(jié)果輸入框的值
document.getElementById("fruit").value=result;
????????}
????</script>
</head>
<body>
<input?type='text'?id='txt1'?/>
<select?id='select'>
????<option?value="+">+</option>
????<option?value="-">-</option>
????<option?value="*">*</option>
????<option?value="/">/</option>
</select>
<input?type='text'?id='txt2'?/>
<input?type='button'?value='?=?'?onclick="count()"/>?<!--通過?=?按鈕來調(diào)用創(chuàng)建的函數(shù)，得到結(jié)果-->
<input?type='text'?id='fruit'?/>
</body>
</html>