Reload a part of php page without refreshing whole page

Question

i\'m using Wordpress as content management system and my template has a div with box class, and contains a dropdown list . my goal is getting the value of this drop

Answer 1

   <select id="select-dropdown">
     <option value="1">Item 1</option>
     <option value="2">Item 2</option>
     <option value="3">Item 3</option>
     <option value="4">Item 4</option>
    </select> 

For this to achieve you should have knowledge of Admin Ajax in wordpress.

Admin Ajax: in your header.php

<script type="text/javascript">
 var ajax_url = '<?php echo admin_url('admin-ajax.php'); ?>';
</script>

in you custom js file

my-custom.js, enqueue the js file

jQuery(document).ready(function(){
  jQuery(body).on('change','#select-dropdown', function(){
     var selected_item  = jQuery(this).val();
     jQuery.ajax({
       type: "POST",
       url: "ajax_url",
       data: {
             action: 'load_posts',
             selected_item: selected_item,
           },
       success: function(res){
         console.log(res);
         //append the result in frontend
         jQuery('.box').html(res);
        },


     })
  })
});

In your function.php

function _boom_load_posts(){
 //get your results here as per selected option
 if(!empty($_POST['selected_item'])){
  $selected_item = $_POST['selected_item'];
  $output = '';
  //rest of the code as per selected_item, store result in $output
  $args = array(

    "meta_query" => array(
            array(
                'key' => 'meta',
                'value' => '$select_value',
                )
        )
);

query_posts( $args );
if ( have_posts() ) : while ( have_posts() ) : the_post();

        $output .= get_the_content();
endwhile; else: 

         $output .= "<p>sorry no post found with this value.</p>"

  endif; 

  echo $output;//you result here
  die(1);
 }
}
add_action('wp_ajax_load_posts', '_dot1_load_posts');
add_action('wp_ajax_no_priv_load_posts', '_dot1_load_posts');

make the required changes, as I can't post the whole code for you, make some efforts and the above code will help you get an idea that how it's going to work.