What is the difference between default and rest parameters in JavaScript functions?

Javascript Web Development Front End Technology

Default Parameters

The default parameter came to handle function parameters with ease. You can easily set Default parameters to allow initializing formal parameters with default values. This is possible only if no value or undefined is passed.

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>

Output

Rest Parameters

ES6 brought rest parameter to ease the work of developers. For arguments objects, rest parameters are indicated by three dots … and precedes a parameter. With this, set indefinite number of arguments as an array, which is Array instances.

Example

Let’s see the following code snippet −

<html>
   <body>
      <script>
         function addition(…numbers) {
            var res = 0;
            numbers.forEach(function (number) {
               res += number;
            });
            return res;
         }
         document.write(addition(3));
         document.write(addition(5,6,7,8,9));
      </script>
   </body>
</html>