我不知道为什么，但只有橙子似乎以我创造的形式计算，但我指定的其他水果没有。我为每个水果指定了每个.value。所有水果的形式在逻辑上与我所看到的相同，所以我不明白为什么我没有得到西瓜或菠萝的结果。
<?xml version = "1.0"?>
<html xmlns = "http://www.w3.org/1999/xhtml">
<head>
<title> Purchase Orange </title>
<!-- Script for the event handlers -->
<script type = "text/javascript">
// The event handler function to compute the cost
function computeCost() {
var orange = document.getElementById("orange").value;
// Compute the cost
document.getElementById("cost").value = orange * 1.99;
var watermelon = document.getElementById("Watermelon").value;
document.getElementById("cost").value = watermelon * 4.99;
var pineapple = document.getElementById("Pineapple").value;
document.getElementById("cost").value = pineapple * 4.69;
} //* end of computeCost
</script>
</head>
<body>
<form>
Orange $1.99/lb <input type = "text" id = "orange" size ="3" />
<br />
</form>
<form>
Watermelon $4.99/lb <input type = "text" id = "watermelon" size ="3" />
<br />
</form>
<form>
Pineapple $4.69/lb <input type = "text" id = "pineapple" size ="3" />
<br />
</form>
<form>
Total Cost is <input type = "text" id = "cost" size ="5" />
<br />
</form>
<form>
<input type = "button" value = "Total Cost" onclick="computeCost();"/>
</form>
</body>
在你的身份证中发现一个简单/资本问题，做了一个小的fiddle，检查一下。
function computeCost() {
var orange = document.getElementById("orange").value;
// Compute the cost
var a = orange * 1.99;
var watermelon = document.getElementById("watermelon").value;
var b = watermelon * 4.99;
var pineapple = document.getElementById("pineapple").value;
var c = pineapple * 4.69;
var total = eval(a + b + c);
document.getElementById("cost").value = total;
} //* end of computeCost
问题是你使用的是错误的ID：
使用：
var watermelon = document.getElementById("watermelon").value;
var pineapple = document.getElementById("pineapple").value;
代替：
var watermelon = document.getElementById("Watermelon").value;
var pineapple = document.getElementById("Pineapple").value;
显示所有计算值的总和。像这样：
var grandtotal =pineapple+ watermelon+orange;
document.getElementById("cost").value = grandtotal;
改变你的身份的情况
var watermelon = document.getElementById("watermelon").value;
var pineapple = document.getElementById("pineapple").value;
我认为这是因为getDocumentById是Key敏感的。你已经写了这样你的身份：pineapple和watermelon你用这样的大写字母检查它们：Pineapple和Watermelon。