Usage of rest parameter and spread operator in JavaScript?

JavascriptWeb DevelopmentFront End Technology

Rest Parameter

With rest parameter, you can represent a number of arguments as an array. ES6 brought rest parameter to ease the work of developers. For arguments objects, rest parameters are indicated by three dots … and precedes a parameter.

Let’s see the following code snippet to define rest parameter −

<html>
   <body>
      <script>
         function addition(…numbers) {
            var res = 0;
            numbers.forEach(function (number) {
               res += number;
            });
            return res;
         }
         document.write(addition(3));
         document.write(addition(9,10,11,12,13));
      </script>
   </body>
</html>

Spread Operator

The spread operator will allow you to split an array into single arguments. These arguments are those, which are the functions as separate arguments.

Syntax

Here’s the syntax −

function myfunction(...iterableObj);

Here’s an example showing Spread Syntax with arguments:

function multiply(x, y) {
   return x*y;
}
var myArgs = [50, 100]; console.log(multiply(…myArgs));

Example

Here’s another example

Live demo

<html>
   <body>
      <script>
         var a, b, c, d, e, f, g;
         a = [10,20];
         b = "rank";
         c = [30, "points"];
         d = "run"

         // concat method.
         e = a.concat(b, c, d);

         // spread operator
         f = [...a, b, ...c, d];
         document.write(e);
         document.write("<br>"+f);
      </script>
   </body>
</html>
raja
Published on 25-Jan-2018 11:30:33
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