It is a good notion to provide a javascript calculator for amount input fields.

Many javascript calculators available on the internet open a separate popup window with keypad and calculator display.

The script provided here will add a calculator icon just after the input fields. Clicking the icon will show the keypad just beneath the input field and the input field will be the 'display' of the calculator.

Click the calculator icon near the input field to open the keypad. Close Field 1 Field 2

To use the script perform the following steps:

• Insert the following javascript and HTML code (adjusting the style of the keypad as neccessary) before the first field of the form (or put in separate file and reference it):

<script type="text/javascript"><!--
/* Script by: www.jtricks.com
 * Version: 20071114
 * Latest version:
 * www.jtricks.com/javascript/forms/calculator.html
 */
var calc_image = '/images/calc.gif';

var calc_start_num = false;
var calc_cur_oper = '';
var calc_acc = 0;
var calc_prev_oper = 0;
var calc_prev_entry = 0;

var calc_field;

function calc_num_value()
{
    if (calc_field.value == '0.')
        return calc_field.value;
    else if (isNaN(calc_field.value))
        return 0;
    else
        return parseFloat(calc_field.value);
}

function calc_perform_oper(oper, val1, val2)
{
    switch(oper)
    {
    case '*':
        return val1 * val2;
    case '/':
        return val1 / val2;
    case '+':
        return Math.round(
                val1 * 10000000000000 +
                val2 * 10000000000000) /
               10000000000000;
    case '-':
        return Math.round(
                val1 * 10000000000000 -
                val2 * 10000000000000) /
               10000000000000;
    default:
        return val2;
    }
}

function calc_press(button)
{
    switch (button)
    {
    case 'CE':
        calc_start_num = true;
        calc_field.value = "0";
        return;

    case 'C':
        calc_acc = 0;
        calc_prev_entry = 0;
        calc_cur_oper = "";
        calc_prev_oper = "";
        calc_start_num = true;
        calc_field.value = "0";
        return;

    case '+/-':
        calc_field.value = calc_num_value() * -1;
        return;

    case ',':
    case '.':
        if (calc_start_num || isNaN(calc_field.value))
        {
            calc_field.value = "0.";
            calc_start_num = false;
        }
        else
        {
            if (calc_field.value.indexOf(".") == -1)
                calc_field.value += ".";
        }
        return;

    case '+':
    case '-':
    case '/':
    case '*':
        calc_prev_oper = button;

        if (calc_start_num)
        {
            calc_cur_oper = button;
            return;
        }

        // No break here.

    case '=':
        calc_start_num = true;

        if (button == '=' && calc_cur_oper != '=')
        {
            calc_prev_entry = calc_num_value();
        }

        if (button == '=' && calc_cur_oper == '=')
        {
            calc_acc = calc_perform_oper(
                calc_prev_oper, calc_acc, calc_prev_entry)
        }
        else
            calc_acc = calc_perform_oper(
                calc_cur_oper, calc_acc, calc_num_value());

        calc_field.value = calc_acc;
        calc_cur_oper = button;

        return;
    }

    if (calc_start_num)
    {
        calc_field.value  = button;
        calc_start_num = false;
    }
    else
    {
        if (calc_num_value() == "0")
            calc_field.value = button;
        else
            calc_field.value += button;
    }
}

function calc_setup(frm, inp)
{
    if (!document.getElementById)
        return;

    document.write(
        '<a href="javascript:void(0);" ' +
        'onclick="calc_show_hide(\'' +
        frm + '\', \'' + inp +
        '\')"><img  style="border:none" ' +
        'src="' + calc_image +
        '"><' + '/a>');
}

function move_box(an, box)
{
    var cleft = 0;
    var ctop = 0;
    var obj = an;

    while (obj.offsetParent)
    {
        cleft += obj.offsetLeft;
        ctop += obj.offsetTop;
        obj = obj.offsetParent;
    }

    box.style.left = cleft + 'px';

    ctop += an.offsetHeight + 2;

    // Handle Internet Explorer body margins,
    // which affect normal document, but not
    // absolute-positioned stuff.
    if (document.body.currentStyle &&
        document.body.currentStyle['marginTop'])
    {
        ctop += parseInt(
            document.body.currentStyle['marginTop']);
    }

    box.style.top = ctop + 'px';
}

function calc_show_hide(frm, inp)
{
    var boxcalc = document.getElementById('attach_calc_div');
    var to_obj = document.forms[frm].elements[inp];

    if (boxcalc == null)
        return;

    if (to_obj != calc_field ||
        boxcalc.style.display=='none')
    {
        // Show and move calculator.

        boxcalc.style.position='absolute';
        move_box(to_obj, boxcalc);
        calc_field = to_obj;
        boxcalc.style.display='block';
    }
    else
        // Hide currently shown calculator.
        boxcalc.style.display='none';
    return false;
}

function calc_hide()
{
    document.getElementById('attach_calc_div')
        .style.display = 'none';
}

//--></script>

<div id="attach_calc_div" style=
 "background:white;border:1px solid #2266AA;display:none">
<form name="attach_calc_form" action=""
 style="margin-bottom:0px;margin-top:0px;padding:2px">

<table style="border:none;padding:0px;border-spacing:0px">

<tbody>

<tr><td></td><td></td><td></td><td></td>
<td align="center"><a style="font-size:9px;color:#2266AA"
 href="javascript:void(0);" onmouseup="calc_hide()">Close</a></td>
</tr>

<tr>
<td><input style="width:40px" name="cbtn7"
 type="button" value="7" onmouseup="calc_press(7)"></td>
<td><input style="width:40px" name="cbtn8"
 type="button" value="8" onmouseup="calc_press(8)"></td>
<td><input style="width:40px" name="cbtn9"
 type="button" value="9" onmouseup="calc_press(9)"></td>
<td><input style="width:40px" name="cbtnp"
 type="button" value="+" onmouseup="calc_press('+')"></td>
<td><input style="width:40px" name="cbtnm"
 type="button" value="-" onmouseup="calc_press('-')"></td>
</tr>

<tr>
<td><input style="width:40px" name="cbtn4"
 type="button" value="4" onmouseup="calc_press(4)"></td>
<td><input style="width:40px" name="cbtn5"
 type="button" value="5" onmouseup="calc_press(5)"></td>
<td><input style="width:40px" name="cbtn6"
 type="button" value="6" onmouseup="calc_press(6)"></td>
<td><input style="width:40px" name="cbtnm"
 type="button" value="*" onmouseup="calc_press('*')"></td>
<td><input style="width:40px" name="cbtnd"
 type="button" value="/" onmouseup="calc_press('/')"></td>
</tr>

<tr>
<td><input style="width:40px" name="cbtn1"
 type="button" value="1" onmouseup="calc_press(1)"></td>
<td><input style="width:40px" name="cbtn2"
 type="button" value="2" onmouseup="calc_press(2)"></td>
<td><input style="width:40px" name="cbtn3"
 type="button" value="3" onmouseup="calc_press(3)"></td>
<td><input style="width:40px" name="cbtnc"
 type="button" value="C" onmouseup="calc_press('C')"></td>
<td><input style="width:40px" name="cbtne"
 type="button" value="CE" onmouseup="calc_press('CE')"></td>
</tr>

<tr>
<td><input style="width:40px" name="cbtn0"
 type="button" value="0" onmouseup="calc_press(0)"></td>
<td><input style="width:40px" name="cbtnd"
 type="button" value="." onmouseup="calc_press('.')"></td>
<td><input style="width:40px" name="cbtnn"
 type="button" value="+/-" onmouseup="calc_press('+/-')"></td>
<td colspan=2><input style="width:84px" name="cbtnq"
 type="Button" value="=" onmouseup="calc_press('=')"></td>
</tr>

</table>
</form>
</div>

• Create a calculator icon or download the sample icon and change the image path in the script (calc_image variable).
• After each field where you want to provide the calculator keypad for you need to add call to calc_setup() function with form name and input name as parameters. For example:

<form name="test" action="">
<input name="inp1"type="text" size="28" value="0">
<script type="text/javascript"><!--
calc_setup('test', 'inp1');
//--></script></form>

• Be sure to verify page design with the Javascript turned off.

The javascript snippet above was tested on the following user agents:

Modern	Firefox 1.5	Ok.
	Firefox 1.0.x	Ok.
	Opera 8.01	Ok.
Steam age	Internet Explorer 6.0	Ok.
	Internet Explorer 5.0	Ok.
Ancient stuff	Netscape Navigator 4.79	Downgrades gracefully *.
	Internet Explorer 4.0	Downgrades gracefully *.
No Javascript or Javascript turned off	Any	Downgrades gracefully *.

*: Graceful degradation means the image with hyperlink to show the calculator keypad will not appear at all and the user will not even know such functionality is on the page.

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