Magento store and display ajax cookie in front end

Question

when user comes first time in a site it will ask for category subcategory etc..after that i store all value into session then if user come to home page it will show it's working fine for all except subcategory

  <?php $tree = $this->helper('techinflo_shop')->getCategoriesDropdown(); ?>
 <?php 
      $categoryvalue = Mage::getSingleton('core/session')->getCategoryValue();
      $attributeValue = Mage::getSingleton('core/session')->getAttributeValue();
      $homecityvalue = Mage::getSingleton('core/session')->getHomeCityValue();
      $subcategoryvalue = Mage::getSingleton('core/session')->getSubCategoryValue();
    ?> 
<script type="text/javascript">
    var children = $H(<?php echo json_encode($tree['children']) ?>);
    function showCat(obj, level) {
        hideContent();
        var catId = obj.value;
        level += 1;
        if ($('cat_container_' + level)) {
            $('cat_container_' + level).remove();
        }
        if (children.get(catId)) {
            var options = children.get(catId);
            //var html = '<select class="form-control" name="subcategory" required="required" id="cat_' + catId + '" onchange="showCat(this, ' + level + ')">';
            var html = '<select class="form-control" name="subcategory" required="required" id="cat_' + catId + '" onchange="showCat()">';
            //html += '<option value=""disabled selected> Select </option>';

            html += '<option value="' + options[i].entity_id + '"' + (options[i].entity_id == '<?php echo $subcategoryvalue?>') ? ' selected="selected"' : '' + '>' + options[i].name + '</option>';  


            for (var i = 0; i < options.length; i++) {
                html += '<option value="' + options[i].entity_id + '">' + options[i].name + '</option>';
            }
            html += '</select>';
            html = '<div id="cat_container_' + level + '">' + html + '</div>';

            $('sub_cat').insert(html);
        }
    }
    //window.onload=showContent();  
     /*function showContent(){
        document.getElementById("default-content").style.display="block";
    }
    function hideContent(){
        document.getElementById("default-content").style.display="none";
    }*/
    function onLoad()
{
    showContent();
    showCat(document.getElementById('first_cat'), 2);
}

window.onload=onLoad();
</script>

<form role="form" method="post" action="<?php echo Mage::getUrl('location/index'); ?>" onsubmit="return validation();">
    <div class="search_content_area">
        <div class="i">
            <span> I am a </span>
        </div>
        <div class="category">
            <select id="first_cat" onchange="showCat(this, 2)" class="form-control" required="required" name="parentcate">
                <option value="" disabled selected>Select</option>
                <?php foreach ($tree['first'] as $cat): ?>
                    <option value="<?php echo $cat->getUrlKey() ?>" <?php echo ($categoryvalue==$cat->getId())?'selected':'' ?>><?php echo $cat->getName() ?></option>
                <?php endforeach ?>
            </select>
        </div>
        <div class="city">
            <span> Shopping City </span>
        </div>
        <div class="select-city">
            <select class="form-control" id="mytext1" required="required" name="homecity">
                <option value="" disabled selected>Select</option>
                <option value="Bangalore" <?php echo ($homecityvalue=='Bangalore')?'selected':'' ?>>Bangalore</option>
                <option value="Calcutta" <?php echo ($homecityvalue=='Calcutta')?'selected':'' ?>>Calcutta</option>
                <option value="Chennai" <?php echo ($homecityvalue=='Chennai')?'selected':'' ?>>Chennai</option>
            </select>
        </div>
        <div class="look">
            <span> Looking For </span>
        </div>
        <div id="sub_cat"></div>
        <div id="default-content">
        <div id="cat_container_va">
          <select class="form-control" id="mytext">
            <option disabled selected>Select</option>
          </select> 
          </div>
        </div>
        <div class="by">
            <span> By </span>
        </div>
        <div class="brand">          
            <select class="attribute-brand form-control" id="attribute" required="required" name="attribute"> 
                  <option>Select</option>
                <?php 
                $attributes = Mage::getModel('catalogsearch/advanced')->getAttributes();
                $attributeArray=array();
                foreach($attributes as $a){
                  if($a->getAttributeCode() == 'brand'){
                    foreach($a->getSource()->getAllOptions(false) as $option){?>
                      <option value="<?php echo $option['value'];?>" <?php echo ($attributeValue==$option['value'])?'selected':'' ?>><?php echo $option['label'];?></option>
                    <?php }
                  }
                }

                ?>
            </select> 
          </div>
        <button class="btn btn-success btn-block let-shop" type="submit">Go</button>
    </div>


    <div style="clear:both"></div>
</form>

Answer 1

I see that when you build the subcategory you do not set a selected value.

html += '<option value="' + options[i].entity_id + '">' + options[i].name + '</option>';  

Try changing it to this:

html += '<option value="' + options[i].entity_id + '"' + (options[i].entity_id == '<?php echo $subcategoryvalue?>') ? ' selected="selected"' : '' + '>' + options[i].name + '</option>';  

I haven't tested the code, so be careful at possible syntax error.

[EDIT]

I see that the subcategories dropdown appears after you call the function showCat on changing the category dropdown.
When the page loads this does not happen.
So you can try to add this code inside your script tag:

function onLoad()
{
    showContent();
    showCat(document.getElementById('first_cat'), 2);
}

And replace the line window.onload=showContent(); with window.onload=onLoad();