Multiply input value on keyup

How do I multiple the value of one input by 2 and save it to another input?

So when I type 10 (for example), the value of the 2nd input will be 20?

Than开发者_运维问答ks

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Two input fields

<input type="text" id="input-value" />
<input type="text" id="output-value" readonly />

And some simple jQuery

var $output = $("#output-value");
$("#input-value").keyup(function() {
    var value = parseFloat($(this).val());
    $output.val(value*2);
});

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Assuming a structure like this:

<input id="inputfield1" type="text" />
<input id="inputfield2" type="text" />

you could use this code:

$("#inputfield1").keyup(function() { // when key is released in "#inputfield1"
// "change()" is also possible instead of "keyup()", slightly different behavior

    var input_value = parseFloat($("#inputfield1").val()); // get number as float
    // alternately parseInt(string, 10), in case you work with integers

    if (!isNaN(input_value)) { // the input is a number
        $("#inputfield2").val(input_value * 2); // update second field
    } else { // the input wasn't a number
        $("#inputfield2").val("not a number?"); // show an error mesage
    }
});

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I think this is what you are looking for:

$('#input-2').val($('#input-1').val() * 2);

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var orgNo = $('#textInput').val();
var newNo = org * 2;
$('#textOutput').val(newNo);