how to substract date object javascript

HTML
Example
<html>
   <head>
      <title>JavaScript setDate Method</title>
   </head>
   <body>
      <script>
         var dt = new Date("December 30, 2017 11:20:25");
         dt.setDate( dt.getDate() - 10 );
         document.write( dt );
      </script>
   </body>
</html>
Output
Wed Dec 20 2017 11:20:25 GMT+0530 (India Standard Time)
Source

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