jquery - Accessing $_POST data in functions.php from a template file after it's been sent via ajax -

i able retrieve data sent via ajax in functions.php. need data in template.php (of theme). first time using ajax , maybe i'm going wrong way. able echo $_post['myvar']; within functions.php (i posting code once work). assuming setup correct, can access ajax data outside of functions.php? btw, signed here @ stack well, if failed follow procedure, apologize.

edited

thanks guys - here sample code. in js file have:

$(window).load(function(){       $("#cat").on("click",function() {            var selectedcat = $(this).children("option").filter(":selected").text();            $.get('../../../../../../wp-admin/admin-ajax.php', {                  action:  "parent_cat_send",                  parent_cat: selectedcat               });            });     }); 

and in functions.php have:

    add_action('wp_ajax_parent_cat_send', 'current_par_cat');    add_action('wp_ajax_nopriv_parent_cat_send', 'current_par_cat');     function current_par_cat() {        global $parent_cat;        $parent_cat = $_get['parent_cat'];        echo $parent_cat;              wp_die();     } 

the response has $parent_cat value. use $parent_cat outside of functions.php i.e in template.php. far, i've tried creating function global variable:

function set_global_var($new_value) {     global $my_global_var;     $my_global_var = $new_value; } 

and calling inside ajax function:

 set_global_var($parent_cat); 

to further explain goal, i'm trying selected value drop-down. value parent category name generated wp_dropdown_categories. after getting it, parent category's sub categories. thought of ajax (which i've never used before) because i'd have 2 drop-down options - 1 parent categories, , other subcategories generated selected parent category(possibly without refreshing page). thanks.

follow step rendor data in template file. there 2 way rendor data can implement same time denpands on situation.

1. you sending ajax request admin panel , want display on frontend
2. you sending ajax request form front end , want display on frontend

if sending ajax request admin panel , want update template(front end) in case first have stroe data in database. said accessed data through functions.php file have update_option() add or update data wordpress database. add have check , fetch in template get_option() rendor on page refresh front end.

now situation two, sending data front end , want update also. in case follow first step update_option() , get_option() , send response functions.php want display in front page(only on same page used send request.) , and display it. if refresh page same updated data rendor on template.

hope understand tried explain.