JavaScript - The Function() Constructor

Quiz

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.

<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

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