Revonzy Mini Shell

$(document).ready(function () {
    function calculate_amount(){
        var var_shirt_price = $("#shirt_price").val();
        var var_shirt_quantity = $("#shirt_quantity").val();
        var var_pant_price = $("#pant_price").val();
        var var_pant_quantity = $("#pant_quantity").val();
        var var_total_amount = $("#total_amount").val();
        var var_discount = $("#discount").val();
        var var_payable_amount = $("#payable_amount").val();
        var var_paid_amount = $("#paid_amount").val();
        var var_balance_amount = $("#balance_amount").val();

        if(isNaN(var_shirt_price)) {
            var_shirt_price = 0;
        }

        if(isNaN(var_shirt_quantity)) {
            var_shirt_quantity = 0;
        }

        if(isNaN(var_pant_price)) {
            var_pant_price = 0;
        }

        if(isNaN(var_pant_quantity)) {
            var_pant_quantity = 0;
        }
       
        var shirt_total_amount = parseFloat(var_shirt_price) * parseFloat(var_shirt_quantity);
        var pant_total_amount = parseFloat(var_pant_price) * parseFloat(var_pant_quantity);
        
        if(isNaN(shirt_total_amount)) {
            shirt_total_amount = 0;
        }

        if(isNaN(pant_total_amount)) {
            pant_total_amount = 0;
        }

        var_total_amount = parseFloat(shirt_total_amount) + parseFloat(pant_total_amount);
        //console.log("**" + var_total_amount);

        if(isNaN(var_total_amount)) {
            var_total_amount = 0;
        }

        if(isNaN(var_discount)) {
            var_discount = 0;
        }

        var_payable_amount = parseFloat(var_total_amount) - parseFloat(var_discount);

        if(isNaN(var_payable_amount)) {
            var_payable_amount = 0;
        }

        if(isNaN(var_paid_amount)) {
            var_paid_amount = 0;
        }

        var_balance_amount = parseFloat(var_payable_amount) - parseFloat(var_paid_amount);

        $("#total_amount").val(var_total_amount);
        $("#payable_amount").val(var_payable_amount);
        $("#balance_amount").val(var_balance_amount);
    }

    $("#shirt_price").keyup(function (e) { 
        calculate_amount();
    });

    $("#shirt_quantity").keyup(function (e) { 
        calculate_amount();
    });

    $("#pant_price").keyup(function (e) { 
        calculate_amount();
    });

    $("#pant_quantity").keyup(function (e) { 
        calculate_amount();
    });

    $("#discount").keyup(function (e) { 
        $("#paid_amount").val(0);
        calculate_amount();
    });

    $("#paid_amount").keyup(function (e) { 

        if(parseFloat($("#paid_amount").val())  > parseFloat($("#payable_amount").val()))
        {
            alert("Paid amount is greater than payable amount");
            $("#paid_amount").val(0);
            calculate_amount();
        }

        calculate_amount();
    });


});