JavaScript - The Function() Constructor

The function statement is not the only way to define a new function; you can define your function dynamically using Function() constructor along with the new operator.

Note − Constructor is a terminology from Object Oriented Programming. You may not feel comfortable for the first time, which is OK.

Syntax

Following is the syntax to create a function using Function( ) constructor along with the new operator.

<script type = "text/javascript">
   <!--
      var variablename = new Function(Arg1, Arg2..., "Function Body");
   //-->
</script>

The Function() constructor expects any number of string arguments. The last argument is the body of the function – it can contain arbitrary JavaScript statements, separated from each other by semicolons.

Notice that the Function() constructor is not passed any argument that specifies a name for the function it creates. The unnamed functions created with the Function() constructor are called anonymous functions.

Example

Try the following example.

Live Demo

<html>
   <head>
      <script type = "text/javascript">
         <!--
            var func = new Function("x", "y", "return x*y;");
            function secondFunction() {
               var result;
               result = func(10,20);
               document.write ( result );
            }
         //-->
      </script>
   </head>
   
   <body>
      <p>Click the following button to call the function</p>
      
      <form>
         <input type = "button" onclick = "secondFunction()" value = "Call Function">
      </form>
      
      <p>Use different parameters inside the function and then try...</p>
   </body>
</html>

Output

javascript_functions.htm