.value問題，求詳細解答
<!DOCTYPE?html>
<html>
?<head>
??<title>?事件</title>??
??<script?type="text/javascript">
???function?count(){
???????var?aValue?=?parseInt(document.getElementById("txt1").value);
???????var?bValue?=?parseInt(document.getElementById("txt2").value);
???????var?aSelect?=?document.getElementById("select").value;
???????var?cValue?=?document.getElementById("fruit");??//???????var?cValue?=?document.getElementById("fruit").value;
???????if(aSelect?==?"+")??????????????????????????????//???????if(aSelect?==?"+")??????????????????????????????
???????{???????????????????????????????????????????????//???????{
??????? cValue.value?=?aValue?+?bValue;????????????//????????????cValue?=?aValue?+?bValue;????????????????
???????}???????????????????????????????????????????????//???????}
???????else?if?(aSelect?==?"-")?
???????{
??????? cValue.value?=?aValue?-?bValue;
???????}
???????else?if(aSelect?==?"/")
???????{
??????? cValue.value?=?aValue?/?bValue;
???????}
???????else
???????{
??????? cValue.value?=?aValue?*?bValue;
???????}???????
???}
??</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>為什么按照注釋的寫法運行沒有效果？.value有什么時候不能加的？
2017-08-12
“?var?cValue?=?document.getElementById("fruit").value
此時是將document.getElementById("fruit").value的值賦值給?var?cValue;
而此時document.getElementById("fruit").value沒有值，
要在?function?count()函數最后寫document.getElementById("fruit").value=var?cValue;此時var?cValue是有值的。
將var?cValue的值賦值給document.getElementById("fruit").value。
2017-08-10
你這fruit是輸出框的id，“?var?cValue?=?document.getElementById("fruit").value”你是這么寫，但是此時他并沒有值