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How can I declare optional function parameters in JavaScript?

To declare optional function parameters in JavaScript, use the “default” arguments. You can try to run the following code to declare optional parameters

Example

Live Demo

<html>
   <body>
      <script>
         // default is set to 1
         function inc(val1, inc = 1) {
            return val1 + inc;
         }
         document.write(inc(10,10));
         document.write("<br>");
         document.write(inc(10));
      </script>
   </body>
</html>