The "Function" Object Type - Functions Are Objects

JavaScript Tutorials - Herong's Tutorial Examples

Dr. Herong Yang, Version 2.20

JavaScript Tutorials - Herong's Tutorial Examples

∟The "Function" Object Type - Functions Are Objects

This section provides a quick description and a tutorial example script on the 'Function' built-in object type, which is used to create functions.

The "Function" object type is a special built-in object type to be used to create new functions. It has the following main features:

New functions can be created with the "Function()" constructor.
All "Function" objects have an inherited property called "length" representing the number of arguments of the function.
All "Function" objects have 3 inherited methods: apply(), call(), and toString().
A "Function" object may have its own properties to share values across multiple calls.
A "Function" object can also be created with a function literal: function name(param...) {body...}.
Of course, a "Function" object can be created in the traditional way - the function declaration statement: function name(param...) {body...}.

function [function_name](parameter_1, parameter_2, ...) { statement_1; statement_2; ... return return_expression };

Here is a tutorial example script showing some of the those features:

// Function_Object_Type.html
// Copyright (c) 2008 by Dr. Herong Yang, http://www.herongyang.com/

   // Creating a new function with the "Function()" constructor
   var sign = new Function("name",
      "this.signature = name;"
      + "sign.count++;"
   )
   
   // Adding an instance property to the function
   sign.count = 0;

   // Checking this object
   println("\nAbout this \"sign\":");
   println("   Type = "+(typeof sign));
   println("   Instance Of Object: "+(sign instanceof Object));
   println("   Instance Of Function: "+(sign instanceof Function));

   // Executing it on the current object
   sign("Herong");

   // Calling it on another object
   var pc = new Object();
   sign.call(pc, "IBM");

   // Checking the signature
   println("\nExecution result:");
   println("   this.signature = " + this.signature);
   println("   pc.signature = " + pc.signature);
   println("   # of calls = " + sign.count);

If you run this script with "jrunscript", you will get:

About this "sign":
   Type = function
   Instance Of Object: true
   Instance Of Function: true

Execution result:
   this.signature = Herong
   pc.signature = IBM
   # of calls = 2

Now we know how to create functions with the "Function()" constructor.

Read other "Function" related chapters to see more tutorial examples.

Table of Contents

About This JavaScript Tutorial Example Book

Introduction to JavaScript

ECMAScript Language Specification and JavaScript Dialects

Data Types, Variables and Expressions

Flow Control Statements

Creating, Accessing, and Manipulating Arrays

Defining and Calling Functions

Web Browser Supporting JavaScript

Server-Side and Client-Side Web Scripting