Which Path should I use in my website? Related path absolute path?

I am building website for my client. I was wondering which path should I use for my website? which path is more secure? also correct me if I am totally wrong or if you have other reason for safety concerns for website! Thanks in advance.

For example...

<script src="https://example.com/admin/js/myjavascript.js"></script>
or
<script src="/js/myjavascript.js"></script>

<img src="https://swadtiffin.ca/wp-content/uploads/myimg.jpg" alt="Loading...!">
or
<img src="/wp-content/uploads/myimg.jpg" alt="Loading...!">

$http({
  method: 'POST',
  url: '/wp-content/themes/astra-child/php/get_all_food_combos.php',
  data: $.param({ 'data': "test" }),
  headers: { 'Content-Type': 'application/x-www-form-urlencoded' }
  }).then(function (resp) {
  console.log(resp.data); //all items
  });
  }, function (error) {
     console.log(error);
  });

or

$http({
  method: 'POST',
  url: 'https://example.com/wp-content/themes/astra-child/php/get_combos.php',
  data: $.param({ 'data': "test" }),
  headers: { 'Content-Type': 'application/x-www-form-urlencoded' }
  }).then(function (resp) {
  console.log(resp.data); //all items
  });
  }, function (error) {
     console.log(error);
  });