javascript formula calculations

Question

I have a rather complex formula that I want to recreate with code, I have set up a fiddle But I have no idea where to start with the JavaScript/jQuery?

Any help to get me started and point me in the right direction would be wonderful.

The formula I need is

(1/(1 - A %)) - 1 = B %
A = Percentage drop (#input)
B = Percentage gain (#output)

For example: If A drops with 25%, B has to increase 33% to break even

I would like the output to be displayed on click of the Calculate div, then in the future I would like to use a jQuery slider to change the input value and have the output change dynamically.

<div id="calc">
<div id="inputlabel">INPUT</div>
<input id="input">%</>
<div id="calculation">CALCULATE</div>
<h1 class="output">%</h1>
</div>

hjpotter92 · Accepted Answer · 2012-10-19T00:13:04.713

3

This code will work:

$(document).ready(function() {
    $('#calculation').click(function() {
        var inp = parseFloat($('#input').val());
        var out = parseFloat((1 / (1 - (inp / 100))) - 1);
        out = parseInt(out * 100);
        $('h1.output').text(out + ' %');
    });
});

Check the updated fiddle.

edited Oct 19 '12 at 00:13

answered Oct 19 '12 at 00:00

hjpotter92

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1

+1 .. Seems to be working fine.. Except the last line where you seem to be prepending .. Better to clear it before prepending.. $('h1.output').empty().prepend(out + '%'); – Sushanth -- Oct 19 '12 at 00:04
@Sushanth-- Ah! `.text(out + ' %')` would've been my preferred choice. (^_^). – hjpotter92 Oct 19 '12 at 00:06
why not `$('h1.output').html(out + ' %')` or `$('h1.output').text(out + ' %')`? – Reflective Oct 19 '12 at 00:11
sorry, didn't saw your comment – Reflective Oct 19 '12 at 00:12

score 1 · Answer 2 · answered Oct 19 '12 at 00:11

Look here for the JSFiddle that does it: http://jsfiddle.net/LC8qE/

function calculate()
{
    var A = parseInt(jQuery('#input').val()) / 100;
    var B = (1/(1 - A)) - 1;
    return Math.round(B * 100);
}

jQuery('#calculation').on('click', function(){
    if(jQuery('#input').val() == '')
        { alert('enter a value!'); return false; }          
    var result = calculate();
    jQuery('.output').text(result + '%');
});

javascript formula calculations

2 Answers2