<!DOCTYPE?html>
<html>
?<head>
??<title>?事件</title>??
??<script?type="text/javascript">
???function?count(){
???????
????//獲取第一個輸入框的值
????var?txt1?=?document.getElementById("txt1").value;
//獲取第二個輸入框的值
????var?txt2?=?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?=?txt1?+?txt2;
???????????break;
????????case?"-":
????????????result?=?txt1?-?txt2;
????????????break;
????????case?"*":
????????????result?=?txt1?*?txt2;
????????????break;
????????case?"/":
????????????result?=?txt1?/?txt2;
????????????break;
????????default?:
????????????break;
????}
????//設置結果輸入框的值?
????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?=?按鈕來調用創建的函數，得到結果-->?
???<input?type='text'?id='fruit'?/>???
?</body>
</html>
2016-07-09
因為：“+”符號被優先當做字符串連接符了，所以效果就是1字符串連接上了2字符串“12”；
修正：加parseInt（）方法強制轉為整數。如：var txt1 = parseInt(document.getElementById("txt1").value);