JavaScript file to add AJAX functionality to your plugin. The 'myAjax.ajaxurl' value is the admin-ajax.php file for your website.

liker_script.js

jQuery(document).ready( function() {
   jQuery(".user_like").click( function(e) {
      e.preventDefault(); 
      post_id = jQuery(this).attr("data-post_id");
      nonce = jQuery(this).attr("data-nonce");
      jQuery.ajax({
         type : "post",
         dataType : "json",
         url : myAjax.ajaxurl,
         data : {action: "my_user_like", post_id : post_id, nonce: nonce},
         success: function(response) {
            if(response.type == "success") {
               jQuery("#like_counter").html(response.like_count);
            }
            else {
               alert("Your like could not be added");
            }
         }
      });
   });
});