[英]Use the value of an input field in calculation, and display the result in another element
我有一個購物車,每個產品都有價格、數量和小計字段。 數量字段可由用戶更改,但其他字段為 static。
當用戶更改數量時,有沒有辦法計算小計? 我想將數量乘以價格,然后更新小計,而不需要用戶提交表單。 此外,在計算小計時,也應更新總計。
我的代碼是一個 Django 模板,看起來像這樣,相關部分在循環中:
<div class="container">
<table id="cart" class="table table-hover table-condensed">
<thead>
<tr>
<th style="width:50%">Product</th>
<th style="width:10%">Price</th>
<th style="width:8%">Quantity</th>
<th style="width:22%" class="text-center">Subtotal</th>
</tr>
</thead>
{% for crops_ordered_names,crops_ordered_images,crops_ordered_cost,crops_ava in total %}
<tbody>
<tr>
<td data-th="Product">
<div class="row">
<div class="col-sm-2 hidden-xs"><img src="http://placehold.it/100x100" alt="..." class="img-responsive"/></div>
<div class="col-sm-10">
<h4 class="nomargin">{{crops_ordered_names}}</h4>
<p>Available amount: {{crops_ava}}</p>
</div>
</div>
</td>
<td data-th="Price" id="price">{{crops_ordered_cost}}</td>
<td data-th="Quantity">
<input type="number" class="form-control text-center" id="quan" min="1" max="{{crops_ava}}">
</td>
<td data-th="Subtotal" class="text-center" id="subtotal"></td>
<td class="actions" data-th="">
<button class="btn btn-danger btn-sm"><i class="fa fa-trash-o"></i></button>
</td>
</tr>
</tbody>
{% endfor %}
<tfoot>
<tr class="visible-xs">
<td class="text-center"><strong>Total 1.99</strong></td>
</tr>
<tr>
<td colspan="2" class="hidden-xs"></td>
<td class="hidden-xs text-center" id="total"><strong>Total </strong></td>
</tr>
</tfoot>
</table>
您需要做的第一件事是對您的 HTML 代碼進行小改動。 由於您將列出多個產品,每個產品都有自己的價格、數量和小計,因此您需要使用class
或數據屬性而不是id
,因為id
對整個文檔是唯一的,並且一個 ID 只能使用一次。 相關代碼(循環內)應如下所示:
<tbody>
<tr>
<td data-th="Product">
<div class="row">
<div class="col-sm-2 hidden-xs"><img src="http://placehold.it/100x100" alt="..." class="img-responsive"/></div>
<div class="col-sm-10">
<h4 class="nomargin">{{crops_ordered_names}}</h4>
<p>Available amount: {{crops_ava}}</p>
</div>
</div>
</td>
<td data-th="Price" data-type="price">{{crops_ordered_cost}}</td>
<td data-th="Quantity">
<input type="number" class="form-control text-center" data-type="quan" min="1" max="{{crops_ava}}">
</td>
<td data-th="Subtotal" class="text-center" data-type="subtotal"></td>
<td class="actions" data-th="">
<button class="btn btn-danger btn-sm"><i class="fa fa-trash-o"></i></button>
</td>
</tr>
</tbody>
您還需要更新表格頁腳,以便總單元格獲得數據屬性:
<td class="text-center" data-type="total"><strong>Total <span>0</span></strong></td>
(需要 span 元素,因此我們只能更新數字。)
下面的示例代碼應該可以解決問題,當數量發生變化時更新小計。 該代碼可能無法在 Internet Explorer 中運行,因此請告訴我是否有此要求。 我還添加了評論以幫助澄清在哪里發生了什么。
// Find all quantity inputs, and the element where we display the total.
const quantityInputs = document.querySelectorAll('[data-type="quan"]');
const total = document.querySelector('[data-type="total"] span');
// For simplicity, we calculate the total in a separate function.
const calculateTotal = () => {
// Find all the subtotals.
const subtotals = document.querySelectorAll('[data-type="subtotal"]');
let calculatedTotal = 0;
// Loop through all the subtotals, and add them to the final total.
Array.from(subtotals).forEach((subtotal) => {
calculatedTotal += Number(subtotal.textContent);
});
// Then return the total.
return calculatedTotal;
}
// As above, we use a separate function to calculate the subtotal for a product.
const calculateSubtotal = (product) => {
// The input event will fire when the value of the quantity field is changed.
product.addEventListener('input', () => {
/*
* With multiple prices and subtototals, we need to look for them going
* upwards from the quantity field, using the parent elements (first the
* table cell, then the table row).
*/
const parentRow = product.parentNode.parentNode;
// Then find the price and subtotal for this product.
const price = parentRow.querySelector('[data-type="price"]');
const subtotal = parentRow.querySelector('[data-type="subtotal"]');
// And finally, update the subtotal and the total.
subtotal.textContent = price.textContent * product.value;
total.textContent = calculateTotal();
});
}
// Loop through all the quantity inputs and wait for the subtotal to change.
Array.from(quantityInputs).forEach((element) => calculateSubtotal(element));
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