Form Validation using JavaScript

Question

I'm trying to validate a form using JavaScript but i'm a bit stuck on displaying a message next to the field to say that "This field is required". How do I go about doing this? Sorry, I'm very new to JavaScript. Here's my js code:

var allFieldsRequired = true;
function specialPostcode(postalCode)
{
 var re = /^[TA]{2}([1-14]|22|15){1,2}/;
 if(re.test(postalCode))
 {
  alert("You have been entered into a competition to win special prize!!");
 }

}

function validatePostcode(postalCode)
{
 var re = /^[A-Z]{2}\d{1,2}\s\d{1}[A-Z]{2}$/;
 if(!re.test(postalCode))
 {
  alert('Postcode is not valid');
 }
 return re.test(postalCode);
}

function validateCard(promoCardNumber)
{
 var re = /^[A-Z]{1}([A-Z]|\d){4}\s?([A-Z]|\d){5}\s?([A-Z]|\d){3}\d{1}$/;
 if(!re.test(promoCardNumber))
 {
  alert('Promotional card number is not valid');
 }
 return re.test(promoCardNumber);
}

function validate(val)
{
 if(val == "")
 {
  return false;
 }
 else
 {
  return true;
 }
}

function verification(orderForm)
{
//set boolean flag
var valid = true;
if(allFieldsRequired)
{
 // validations
 if(valid)
 {
  valid = validatePostcode(orderForm.postalCode.value);
 }
 if(valid)
 {
  valid = validateCard(orderForm.promoCardNumber.value);
 }
 if(valid)
 {
  valid = validate(orderForm.firstName.value);
 }
 if(valid)
 {
  valid = validate(orderForm.surname.value);
 }
 if(valid)
 {
  valid = validate(orderForm.phoneNumber.value);
              }
 if(valid)
 {
  valid = validate(orderForm.streetName.value);
 }
 if(valid)
 {
  valid = validate(orderForm.city.value);
              }                                                          
    if(valid)
 {
  valid = validate(orderForm.billEmailAddress.value);
 }
 if(valid)
 {
  valid = validate(orderForm.billPhoneNumber.value);
 }
 if(valid)
 {
  valid = validate(orderForm.billCardNumber.value);
 }
 if(valid)
 {
  specialPostcode(orderForm.postalCode.value);
    }

}
else
{
 // validations
 if(valid)
 {
  valid = validatePostcode(orderForm.postalCode.value);
 }
 if(valid)
 {
  valid = validateCard(orderForm.promoCardNumber.value);
 }
 if(valid)
 {
  specialPostcode(orderForm.postalCode.value);
 }
}
return valid;
} // end of verification

This is my HTML code for the form:

<form id="orderForm" method="post" action="x">
   <table id="formTable" cellpadding="5">
    <tr>
     <td>
      <h3>Shipping and Billing Information</h3>
     </td>
     <td>&nbsp;</td>
    </tr>
    <tr>
     <td>First Name</td>
     <td><input id="firstname" type="text" name="firstName" maxlength="30" /></td>
    </tr>
    <tr>
     <td>Surname</td>
     <td><input id="surname" type="text" name="surname" maxlength="30" /></td>
    </tr>
    <tr>
     <td>Contact Telephone Number</td>
     <td><input id=phoneNumber" type="text" name="phoneNumber" maxlength="30" /></td>
    </tr>
    <tr>
     <td>Street Name</td>
     <td><input id="streetName" type="text" name="streetName" maxlength="30" /></td>
    </tr>
    <tr>
     <td>City</td>
     <td><input id="city" type="text" name="city" maxlength="30" /></td>
    </tr>
    <tr>
     <td>Postal Code</td>
     <td><input id="postalCode" type="text" name="postalCode" maxlength="30" /></td>
    </tr>
    <tr>
     <td>Email address</td>
     <td><input id="emailAddress" type="text" name="emailAddress" maxlength="30" /></td>
    </tr>
    <tr>
     <td>Contact Telephone Number</td>
     <td><input id="billPhoneNumber" type="text" name="billPhoneNumber" maxlength="30" /></td>
    </tr>
    <tr>
     <td>Promotional card</td>
     <td><input id="promoCardNumber" type="text" name="promoCardNumber" maxlength="30" /></td>
    </tr>
    <tr>
     <td>Credit Card Number</td>
     <td><input id="billCardNumber" type="text" name="billCardNumber" maxlength="30" /></td>
    </tr>
    <tr>
     <td>Credit Card Type</td>
     <td>
      <select id="billCardType" name="billCardType">
       <option value="...">
        Choose your card...
       </option>
       <option value="visa">
        Visa
       </option>
       <option value="mastercard">
        Mastercard
       </option>
      </select>
     </td>
    </tr>
    <tr>
     <td>Instructions</td>
     <td><textarea id="instructions" name="instructions" rows="8" cols="30">Enter your requirements here or comments.</textarea></td>
    </tr>
    <tr>
     <td colspan="2"><input id="submit" type="submit" name="Submit" value="Submit" onclick="return verification(document.getElementById('orderForm'));" /></td>
    </tr>
   </table>
  </form>

Answer 1

Add a span near each field so you can use it for the validation message:

<td>First Name</td>
<td>
  <input id="firstname" type="text" name="firstName" maxlength="30" />
  <span id="firstname_error"/>
</td>

After that, just add the error message there, so instead of:

alert('You need to complete this field')

You would use:

document.getElementById('firstname_error').innerHTML = 'You need to complete this field'

Answer 2

Your way of validation form fields is absolutely terrible, a lot of unneded and bloated code which is not optimized at all.

I will strongly reccomend you use some sort of readyly available FormValidation script or have a look at this jQuery plugin
Using jQuery your code can look like this (plus you also get the messages to appear next to field):

$("#signupForm").validate({
 rules: {
  firstname: "required",
  lastname: "required",
  username: {
   required: true,
   minlength: 2
  },
  password: {
   required: true,
   minlength: 5
  },
  confirm_password: {
   required: true,
   minlength: 5,
   equalTo: "#password"
  },
  email: {
   required: true,
   email: true
  }
 }
})

Answer 3

Simplest way is to put a hidden span tag below the input field like so

<input .... /> <br />
<span id="fieldname" style="display: none;">This field is required</span>

In Javascript you can do this

if(!valid)
{
  document.getElementById("fieldname").style = "block";
}