Javascript disable right click

<script type="text/javascript">

function md(e)
{
  try { if (event.button==2||event.button==3) return false; }
  catch (e) { if (e.which == 3) return false; }
}
document.oncontextmenu = function() { return false; }
document.ondragstart   = function() { return false; }
document.onmousedown   = md;

</script>

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