trying to toggle a boolean variable with a button

im trying to toggle a variable with a button the code doesnt toggle it only outputs what the variable initially was

<button id="lock" onclick="togle()">
  <img id="img1" src="images/lock.png" class="center" >
  <script>
  var mode = false;
function togle(){
  if (mode == true) {
     mode = false;
   } else {
     mode = true;
   }
 }
  </script>

result is always the default variable

the variable should toggle between true and false but it just stays what it is