Javascript：检测复选框是否检查不起作用

Question

我已经阅读了所有的教程，并且一直在努力尝试让它发挥作用。

onClick 可以正常触发，但它永远不会进入 IF 循环，它会检查复选框是否已被选中。

<!DOCTYPE html>
<html>
<head>
</head>

<header>
<script>

function updateTotal() {
document.orderform.total.value = 1*document.orderform.subtotal.value + 1*document.orderform.tax.value + 1*document.orderform.shipping.value;
}

**function applyDiscount(x) {


if (document.orderform.getElementById(x).checked == true) {
alert("Made it in if");
document.orderform.subtotal.value = .7*document.orderform.subtotal.value;
updateTotal();
}**

}

</script>
</header>

<body>


<section>
<h1>H1 here</h1>

<article>
<p>Article text here</p>
</article>

<form name="orderform" id="orderform" method="post" action="result.php">

<label for="firstname">First Name</label>
<input type="text" name="firstname" id="firstname" placeholder="Enter First Name Here" />
<br />


<label for="subtotal">Subtotal</label>
<input type="text" name="subtotal" id="subtotal" value="10" onChange="updateTotal()"/>
<br />

<label for="shipping">Shipping</label>
<input type="text" name="shipping" id="shipping" value="2" onChange="updateTotal()"/>
<br />

<label for="tax">Tax</label>
<input type="text" name="tax" id="tax" value="1" onChange="updateTotal()" />
<br />

<label for="total">Total</label>
<input type="text" name="total" id="total" value="13" />
<br />

<label for="discountbox">Apply 30% discount</label>
<input type="checkbox" name="discountbox" id="discountbox" onClick="applyDiscount(this.id)"/>

<input type="submit" name="submit" />

</form>

</section>

<footer>
<p>Footer here</p>
</footer>


</body>

Answer 1

你能试着把这个条件放在一边

if (document.getElementById('discountbox').checked == true)

Answer 2

问题是您的 document.orderform 是您的表单，而 getElementById 在文档中。

你可以这样做：

document.getElementById(x).checked

或：

document.orderform.elements[x].checked

Answer 3

尝试一些更简单的东西：

if (document.getElementById(x).checked)

Answer 4

有几处是错误的：

1. 应该在标签中。
2. 行 document.orderform.getElementById 需要是 document.getElementById

这在 chrome 中对我有用：

<!DOCTYPE html>
<html>
<head>

<script>

function updateTotal() {
document.orderform.total.value = 1 * document.orderform.subtotal.value + 1 * document.orderform.tax.value + 1 * document.orderform.shipping.value;
}

function applyDiscount(x) {


if (document.getElementById(x).checked == true) {
alert("Made it in if");
document.orderform.subtotal.value = .7 * document.orderform.subtotal.value;
updateTotal();
}

}

</script>

</head>
<body>
<header>
Header Goes here.
</header>

<section>
<h1>H1 here</h1>

<article>
<p>Article text here</p>
</article>

<form name="orderform" id="orderform" method="post" action="result.php">

<label for="firstname">First Name</label>
<input type="text" name="firstname" id="firstname" placeholder="Enter First Name Here" />
<br />


<label for="subtotal">Subtotal</label>
<input type="text" name="subtotal" id="subtotal" value="10" onChange="updateTotal()"/>
<br />

<label for="shipping">Shipping</label>
<input type="text" name="shipping" id="shipping" value="2" onChange="updateTotal()"/>
<br />

<label for="tax">Tax</label>
<input type="text" name="tax" id="tax" value="1" onChange="updateTotal()" />
<br />

<label for="total">Total</label>
<input type="text" name="total" id="total" value="13" />
<br />

<label for="discountbox">Apply 30% discount</label>
<input type="checkbox" name="discountbox" id="discountbox" onClick="applyDiscount(this.id)"/>

<input type="submit" name="submit" />

</form>

</section>

<footer>
<p>Footer here</p>
</footer>


</body>
</html>

Answer 5

我相信这就是你的意思：

<script>

function updateTotal() {
    document.getElementById("total").value = 1*document.getElementById("subtotal").value + 1*document.getElementById("tax").value + 1*document.getElementById("shipping").value;
}

function applyDiscount(x) {


if (document.getElementById(x).checked == true) {
    document.getElementById("subtotal").value = .7 * document.getElementById("subtotal").value;
    updateTotal();
    }

}