// JavaScript Document
document.write("<form name=\"MortgageMinder\" id=\"mform\">");

document.write("<fieldset>");

document.write("<legend>Mortgage Details</legend>");

document.write("<label>House Price</label>");

document.write("<div><input type=\"text\" name=\"price\" id=\"price\" value=\"200000\" onBlur=\"checkForZero(this)\" onChange=\"checkForZero(this)\" class=\"input\" /></div><br />");

document.write("<label>Deposit</label>");

document.write("<div><input type=\"text\" name=\"dp\" value=\"0\" onChange=\"calculatePayment(this.form)\" class=\"input\" /></div><br />");

document.write("<label>Interest Rate</label>");

document.write("<div><input type=\"text\" name=\"ir\" value=\"7.5\" onBlur=\"checkForZero(this)\" onChange=\"checkForZero(this)\" class=\"input\" /></div><br />");

document.write("<label>Term (Years)</label>");

document.write("<div><input type=\"text\" name=\"term\" value=\"30\" onBlur=\"checkForZero(this)\" onChange=\"checkForZero(this)\" class=\"input\" /></div><br />");

document.write("</fieldset>");

document.write("<fieldset>");

document.write("<legend>Your Results</legend>");

document.write("<label>Mortgage Payable</label>");

document.write("<div><input type=\"text\" name=\"principle\" class=\"input\" /></div><br />");

document.write("<label>No Of Payments</label>");

document.write("<div><input type=\"text\" name=\"payments\" class=\"input\" /></div><br />");

document.write("<label>Monthly Payment</label>");

document.write("<div><input type=\"text\" name=\"pmt\" class=\"input\" /></div>");

document.write("</fieldset>");

document.write("</form>");



// code adapted from http://www.mcfedries.com/CreatingAWebPage/mortgage.htm



function checkForZero(field)

{

    if (field.value == 0 || field.value.length == 0) {

        alert ("This field can't be 0!");

        field.focus(); }

    else

        calculatePayment(field.form);

}



function cmdCalc_Click(form)

{

    if (form.price.value == 0 || form.price.value.length == 0) {

        alert ("The Price field can't be 0!");

        form.price.focus(); }

    else if (form.ir.value == 0 || form.ir.value.length == 0) {

        alert ("The Interest Rate field can't be 0!");

        form.ir.focus(); }

    else if (form.term.value == 0 || form.term.value.length == 0) {

        alert ("The Term field can't be 0!");

        form.term.focus(); }

    else

        calculatePayment(form);

}



function calculatePayment(form)

{

    princ = form.price.value - form.dp.value;

    intRate = (form.ir.value/100) / 12;

    months = form.term.value * 12;

    form.pmt.value = Math.floor((princ*intRate)/(1-Math.pow(1+intRate,(-1*months)))*100)/100;

    form.principle.value = princ;

    form.payments.value = months;

}