HTML Text Input * “value”; display in different text input

Question

I've been looking for an answer to this issue but cannot find one. I'm attempting to input a number into a html input tag with the type being 'text'. I then need that value that's placed into that input multiplied by 2 and the answer displayed into another input.

My table looks like this. This is then repeated multiple times and closed with the appropriate table tag.

<table class="left-table" style="width:50%">

        <th><u>Expense</u></th>
        <th><u>Weekly</u></th>
        <th><u>Fortnightly</u></th>
        <th><u>Yearly</u></th>

        <tr>
            <td class="options">
                <select class="expense-option">
                    <option>- Select Option -</option>
                    <option>Car Insurance</option>
                    <option>Car Loan</option>
                    <option>Car Park</option>
                    <option>Car Registration</option>
                    <option>Car Servicing</option>
                    <option>Clothes</option>
                    <option>Credit Card</option>
                    <option>Dining Out</option>
                    <option>Donation</option>
                    <option>Entertainment</option>
                    <option>Groceries</option>
                    <option>Health Insurance</option>
                    <option>Internet</option>
                    <option>Mobile Phone</option>
                    <option>Petrol</option>
                    <option>Rent / Mortgage</option>
                    <option>Spending / Pocket Money</option>
                    <option>Sport</option>
                    <option>Utilities</option>
                </select>
            </td>

            <td><input class="amount" id="input10" type="text" placeholder="Weekly $"></td>
            <td><input class="amount" id="output10" type="text" placeholder="Fortnightly $" readonly></td>
            <td><input class="amount" id="output20" type="text" placeholder="Yearly $" readonly></td>  

        </tr>

My JS is like this:

    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>
<script>
$("#input10").keyup(function(){
 var input1 = parseInt($("#input10").val());
 if(!isNaN(input1)){
     $("#output10").val(input1 * 2);
 }
 else{
     $("#output10").val("");
     alert("Please enter a valid number");
 }
});
</script>

But still nothing works.

Answer 1

 $("#input1").keyup(function(){ var input1 = parseInt($("#input1").val()); if(!isNaN(input1)){ $("#output1").val(input1 * '2'); } else{ $("#output1").val(""); alert("Please enter a valid number"); } }); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <table> <tr> <td><input class="amount" id="input1" type="text" placeholder="Weekly $"></td> <td><input class="amount" id="output1" type="text" placeholder="Fortnightly $" readonly></td> </tr> </table> 

 $("#input1").keyup(function(){ var input1 = parseInt($("#input1").val()); if(!isNaN(input1)){ $("#output1").val(input1 * '2'); } else{ $("#output1").val(""); alert("Please enter a valid number"); } }); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <table> <tr> <td><input class="amount" id="input1" type="text" placeholder="Weekly $"></td> <td><input class="amount" id="output1" type="text" placeholder="Fortnightly $" readonly></td> </tr> </table> 

you have a typo in the first line (also assuming you have a table structure of this :

<td><input class="amount" id="input1" type="text" placeholder="Weekly $"></td>
<td><input class="amount" id="output1" type="text" placeholder="Fortnightly $" readonly></td>

remove the ' characters around the 2 in the line:

$("#output1").val(input1 * '2');

this makes it a string you need (in order to keep it a number that can be used for the calculation:

$("#output1").val(input1 * 2);

The corrected working code is (table structure added):

    <table>
        <tr>
            <td><input class="amount" id="input1" type="text" placeholder="Weekly $"></td>
            <td><input class="amount" id="output1" type="text" placeholder="Fortnightly $" readonly></td>
        </tr>
    </table>


<script>
$("#input1").keyup(function(){
 var input1 = parseInt($("#input1").val());
 if(!isNaN(input1)){
     $("#output1").val(input1 * 2);
 }
 else{
     $("#output1").val("");
     alert("Please enter a valid number");
 }
});
</script>

Answer 2

Here you have parsed the string to int

var input1 = parseInt($("#input1").val());

But in appending the value , you are trying to multiple with string 2 as it is enclosed inside '' . So solution of this is very simple, u need to multiple with int value .ie. 2 only.

var result = input1 * 2 ;
$("#output1").val(result);