Changing the Element Properties on fly , example making a field required or optional on fly

• Create an page item in apex called AGE.
• Add the span tag to thew item label along with the label of the item as  
• <
  span id="P1_AGE"
  >
  Age of Customer
  :
  <
  /span
  >

Now in case you want to make the age as mandatory field depending on any other field lets call it as ...Admission_class .

In case the Admission_class field is as play school then the age is not required to be made as mandatory and in the case when admission_class is choosen as  KG then this field AGE needs to be made as mandatory.

So lets create one more item called p1_admission_Class .

Lets call a javascript on the change of the field admission_Class to make the other field as mandatory.

function show_fields_mandatory(v1)
{
if (v1=='PLAY SCHOOL')
{

// alert(v1);
var x=document.getElementById("P1_Admission_class');
x.style.color = 'red';
}

if (v1=='KG')
{

// alert(v1);
var y=document.getElementById("P1_ADMISSION_CLASS");
var x=document.getElementById("P1_AGE");

x.style.color = 'black';
y.selectedIndex = 0;

}

}

call this javascript on the admission_class field .