Simple Percentage Calculation Of An Input Field With Jquery

I'm building a PayPal form that the user enters the amount and after that transfered to paypal, everything is working fine but i need to add a calculation plugin to do the followin

Solution 1:

Is there a reason you use jQuery() instead of $()?

Also, you should really cache your selected elements so you don't have to query the DOM multiple times for the same element.

Here's how I would do it:

$(function() {
    // the minimum required value to be entered.// in this case PayPal takes $0.35 from a $1// donation, hence we ask for at least $1.35var minimum_value = 1.35;

    // cache elements that are used at least twicevar$amount = $("#input_amount"),
        $msg = $("#msg"),
        $commission = $("#site_commission_box");

    // attach handler to input keydown event$amount.keyup(function(e){
        if (e.which == 13) {
            return;
        }
        var amount = parseFloat($amount.val()),
            commission = amount*0.02;

        if (isNaN(commission) || isNaN(amount)) {
            $msg.hide();
            $commission.hide();
            return;
        }

        if (amount <= minimum_value) {
            $commission.hide();
            $msg
                .text("PayPal takes $0.35 commission for a $"+amount+" donation.")
                .fadeIn();
        } else {
            $msg.hide();
            $commission
                .fadeIn()
                .find("span")
                    .text((amount-commission).toFixed(2));
        }
    });

    // attach handler to the form submit event
    $('#form_paypal').submit(function() {
        // check if there is an amount enteredif ($amount.val() > null) {
            // is the amount equal to or higher than the minimum_value?if ($amount.val() < minimum_value) {
                // need more amount// show more amount error$msg
                    .addClass("icon_warning_red")
                    .text("Please enter an amount and try again.")
                    .fadeIn();
                returnfalse; // prevent the form from submitting
            }
            else {
                // amount is more than minimum_value// show activity$msg
                    .removeClasss("icon_warning_red")
                    .html('<img src="loader.gif" align="middle" alt="load"/>&nbsp;Transferring to PayPal, please wait...')
                    .fadeIn();
                returntrue; // submit the form
            }
        }
        else {
            // no amount entered at all// show no amount error;$msg.addClass("icon_warning_red").fadeIn();
            returnfalse; // prevent the form from submitting
        }
    });
});

You can see a working example here, there you can see the changes I did in the HTML as well.

Solution 2:

You have to add a event-handler for a change event. Everytime if the input value is changed the discount is recalculated. See an example on http://jsfiddle.net/3sXZw/