大佬們，為什么這個沒有結果，哪兒出問題了？
<!DOCTYPE?html>
<html?lang="en">
<head>
????<meta?charset="UTF-8">
????<meta?name="viewport"?content="width=device-width,?initial-scale=1.0">
????<meta?http-equiv="X-UA-Compatible"?content="ie=edge">
????<title>Document</title>
????<script?type="text/javascript">
????????function?count()?{
????????????//獲取第一個輸入框的值
????????????var?num1?=?parseInt(document.getElementById("txt1").value);
????????????//獲取第二個輸入框的值
????????????var?num2?=?parseInt(document.getElementById("txt2").value);
????????????//獲取選擇框的值
????????????var?num3?=?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
????????????//設置結果輸入框的值?
????????????var?sum?=?"";
????????????switch?(num3)?{
????????????????case?"+":
????????????????????sum?=?num1?+?num2;
????????????????????break;
????????????????case?"-":
????????????????????sum?=?num1?-?num2;
????????????????????break;
????????????????case?"*":
????????????????????sum?=?num1?*?num2;
????????????????????break;
????????????????case?"/":
????????????????????sum?=?num1?/?num2;
????????????????????break;
????????????}
????????????document.getElementById("fruit").value?=?sum;
????????}
????</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(chuàng)建的函數(shù)，得到結果-->
????<input?type='text'?id='fruit'?onclick="count()"?/>
</body>
</html>
2020-01-11
居然時把??document.getElementById("fruit").value?=?sum; 的Id寫成ld的原因。