如何使用JavaScript更新按键上的文本框

Question

Is there a way to update the value of a textbox on every key press?

I'm doing currency conversion. So, there are two textboxes, one for the user to input the value while the other will automatically show the converted amount on every key press.

Should I use a for loop? But what should I loop?

The textboxes in the following for loop should be able to do its individual row conversion

<% for(int i=0; i<2; i++) { %>
 <td><input type="text" id= "amount" name="amount<%=i%>" /></td>

 <td><input type="text" id= "convertedAmount" name="convertedAmount<%=i%>" readonly/></td>
<%}%>

How should I get started in attempting this task?

Thanks in advance for any possible help.

Answer 1

onkeyup is best suited for your task:

Type amount $: <input type='text' id='amount' onkeyup="updateConverted()" >
<br>
Converted: <input type='text' id='converted' >

JavaScript function:

function updateConverted() {
    var conversionRate = 1.5;
    document.getElementById('converted').value =
                       document.getElementById('amount').value * conversionRate;
}

Demo here .

---

Update (JSP for loop):

In the case of your for loop, you can just use the following jQuery code (no need to change the HTML):

$('input[name=amount]').each(function (_, value) {
    $(value).keyup(function () {
        var rate = 1.5;
        var convAmount = $(this).val() * rate;
        $(this).parent().next().children('input[name=convertedAmount]').val(convAmount);
    });
});

See demo here .

_{Note: Your for loop is generating duplicated IDs. If possible, avoid that as it is invalid HTML.}

Answer 2

Simple using jQuery:

<input type="text" name="t1" id="t1" value="" onkeypress="calculation()" />

<input type="text" name="converted" id="converted" value="" />

<script>
function calculation() {
   var price = 'here is your formula';
   $('#converted').val(price);
}
</script>