How to get post id by id on click

I’d add a data-id attribute to the anchor element that I’m trying to fetch. In order to keep things SEO friendly, make sure you have a fallback template for the full URL.
<a href="mysite.com/portfolio/my-item" data-id="1432">View portfolio entry</a>
Then, in jQuery, you can fetch the id via:

jQuery(function($) {
  $("[data-id]").on('click', function  (){
    var id = $(this).data('id');
    //Use id for JSON API now :-)
   })
})