[Dilettante_Pro]

<img src="https://pbs.twimg.com/profile_images/473506797462896640/_M0JJ0v8.png" width="200" height="200" alt="" id="nkar" onclick='zoom()'>
<script>
var elem = document.querySelector('img'),
      sign = 1,
      stepSize = 50,
      minSize = 200,
      maxSize = 500,
      curSize;
elem.onclick = function() {
   curSize = elem.width + stepSize * sign;
   elem.width = curSize;
   elem.height = curSize;
   if(curSize == minSize || curSize == maxSize) sign = -sign;
}
</script>

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