php - show div with forms when customer starts typing in first form

Solution:

You have to do it in javascript (client-side) I would recommand you to use a library like jquery it'll be easier.

<script type="text/javascript">
//with jQuery
$(document).ready(function(){

  //admiting that the input[name=CompanyName] is the one you want to bind with the div
  $('#NewCustomerDiv input[name=CompanyName]').keyup(function(){
   //admiting that the div you want to show is CustomerCompanyDiv
   if(!$(this).val()){
     $('#CustomerCompanyDiv').hide();
   }
   else{
     $('#CustomerCompanyDiv').show();
   }
  });
  if($('#NewCustomerDiv input[name=CompanyName]').val()){
     $('#CustomerCompanyDiv').show(); 
  }
});
</script> 

<div id="NewCustomerDiv" >
<label>Company name: </label>
<input type="text" name="CompanyName" value="<?php echo $customer['CompanyName']; ?>"/>
<br />

<div id="CustomerCompanyDiv" >    <label>Company name:</label>
  <input type="text" name="CompanyNumber" value="<?php if(isset($customer['CompanyNumber'])){ echo $customer['CompanyNumber']; } ?>"/>
  <br />

  <label>taxnumber:</label>
  <input type="text" name="TaxNumber" value="<?php if(isset($customer['TaxNumber'])){ echo $customer['TaxNumber']; } ?>"/>
  <br />

  <?php if(count($array_legaltype) > 0){ ?>
  <label>companytax:</label>
  <select name="LegalForm" >
    <?php foreach($array_legaltype as $k=>$v){ ?>
      <option value="<?php echo $k; ?>" <?php if(isset($customer['LegalForm']) && $customer['LegalForm'] == $k){ echo "selected=\"selected\""; } ?>><?php echo $v; ?></option>
    <?php } ?>
  </select>
  <br />
  <?php } ?>

  <br />
</div>
</div>
Copy code

See it in action : http://jsfiddle.net/TMG85/