Javascript：数量变化时更新价格

Question

我是javascript的新手，我已经从事此工作4天了，但没有取得任何进展。 我尝试了很多不同的选择。 我看到像我这样的例子奏效了……但它对我没有用。 :(我正在尝试随着门票数量的变化而调整价格。以下是javascript，而以下是html。非常感谢您的协助！谢谢！

document.getElementById("totalTicketCost").value = 0 + "." + 00;

function ticketCost()


{

var ticketCost = 5.5;

var inputTicketQuantity = document.getElementById("inputTicketQuantity").value;

var totalTicketCost = parseFloat(ticketCost) * inputTicketQuantity;



if (!isNaN(totalTicketCost))





document.getElementById("totalTicketCost").innerHTML = totalTicketCost;



}

    <form onsubmit="" ="return alertDetails()" id="formPurchaseTickets" enctype="text/plain" method="post" action="mailto:cmst388@xyz.com">
        <h1>Ticket Purchasing Form</h1>
        <p class="alert">Act fast! This transaction must be completed in <span id="timer"></span> minutes.</p>
        <div class="field">
            <label class="required">How many tickets would you like to purchase?</label>
            <input id="inputTicketQuantity" tabindex="1" required type="number" value="0" name="ticket-quantity" min="1" max="3" step="1" title="You can only buy between 1 and 3 tickets">
            $<span id="totalTicketCost">0.00</span>
        </div>

        <div id="contactInfo" style="display:none;">
            <div class="field">
                <label class="required">Name:</label>
                <input required name="name" tabindex="2" type="text" placeholder="Enter name" pattern="[a-zA-Z\s]+" title="Enter only letters. e.g. Smith">
            </div>

            <div class="field">
                <label class="required">E-mail:</label>
                <input id="inputEmail" tabindex="3" required name="email" type="email" placeholder="Enter e-mail address"  onblur="validateEmail()">
            </div>
        </div>
        <hr>

        <input type="submit" tabindex="4" value="Purchase Tickets"> <input type="reset">
    </form>



    <script src="event_registration.js"></script>

</body>

Answer 1

在这里仅使用ES5（假设您目前不在转译中），我做了一个快速重构。

var ticketInput = document.getElementById("totalTicketCost");
var inputTicketQuantity = document.getElementById("inputTicketQuantity");
var ticketCost = 5.5;

// Handle the precision up to >= $100
function changeCost( num ) {
  var cost = new Number( parseFloat( num ) * ticketCost );
  var precision = cost.toString().length === 3 ? 3 : 4;
  return cost.toPrecision( precision );
}

inputTicketQuantity.addEventListener('input', function( event ) {
  var value = event.target.value;
  if ( !isNaN( value ) ) {
    ticketInput.innerHTML = changeCost( value );
  }
});

您绝对想尽可能地将JS与HTML分开，避免难以阅读的内联内容，例如<form onsubmit="" ="return alertDetails()" ，至少应为<form onsubmit="return alertDetails()"修复。

Answer 2

将事件侦听器添加到“数量”字段中，然后重新计算价格。

document.querySelector("#inputTicketQuantity").addEventListener("input", function() {
  let count = this.value;
  calculatePrice(count);
});

Answer 3

您必须在输入数量文本框的值更改事件上调用函数ticketCost()

<input id="inputTicketQuantity" onkeydown="ticketCost()" tabindex="1" required type="number" value="0" name="ticket-quantity" min="1" max="3" step="1" title="You can only buy between 1 and 3 tickets">

或者您可以在JavaScript中添加侦听器为

document.getElementById("inputTicketQuantity").addEventListener("onkeydown", ticketCost);

将其添加到您的JavaScript函数ticketCost（）之外

Answer 4

您的问题不是很明确地针对您要实现的目标，但是此处提供了在用户添加凭单时更新总费用的功能-

在JS中：

function updateCost(count)
{
   var ticketCost = 5.5;
   document.getElementById("totalTicketCost").innerHTML = count * ticketCost;
}

在HTML中

<input id="inputTicketQuantity" tabindex="1" required type="number" value="0" name="ticket-quantity" onchange="updateCost(this.value)" min="1" max="3" step="1" title="You can only buy between 1 and 3 tickets">