respimg_currentSrc.html

<img id="test" sizes="100vw" srcset="img.jpg 500w" alt="">
  
<script>
    document.addEventListener("DOMContentLoaded", function() {
       var test = document.getElementById("test");
       test.addEventListener("load", function() {
          console.log("Current Src: " + test.currentSrc);
       });  
    });
</script>