OnOff Light

<html>
  <body>
    <img id="testimg" src="https://www.w3schools.com/js/pic_bulboff.gif" />

      <button onclick="lightonfunction();">Light On</button>

      <button onclick="lightofffunction();">Light Off</button>


    <script>
      function lightonfunction(){
        document.getElementById('testimg').src = "https://www.w3schools.com/js/pic_bulbon.gif";
      }
      function lightofffunction(){
        document.getElementById('testimg').src = "https://www.w3schools.com/js/pic_bulboff.gif";
      }

    </script>
  </body>
</html>