Defining Your Own Functions - Example

This section provides a tutorial example on how to define your own JavaScript functions.

Here is a JavaScript tutorial example of defining a user function.

<html>
<!-- Define_Functions.html
   Copyright (c) 2013 by Dr. Herong Yang, herongyang.com
-->
<head><title>Define Functions</title></head>
<body>
<pre>
<script type="text/javascript">
// Defining a null function that does nothing
function null() {
}

// Defining a simple function
function hello() {
   document.write('Hello World!');
}

// Defining a function to convert Fahrenheit to Celsius
function f2c(fahrenheit) {
   document.write("Converting Fahrenheit = "+fahrenheit+"\n");
   var celsius = (fahrenheit - 32.0 ) / 1.8;
   document.write("Returning Celsius = "+celsius+"\n");
   return celsius;
}
</script>
</pre>
</body>
</html>

If you run this JavaScript page in a Web browser, you will get a blank window, because it only defines 3 functions. But it does not call any of them to run. Therefore no statement gets executed.

The first function null() is defined to do absolutely nothing.

The second function hello() is defined to write "Hello World!" into the HTML document.

The third function f2c() is defined to do a couple of things: taking a parameter "fahrenheit", declaring a local variable "celsius", assigning "celsius" with the Celsius value converted from "fahrenheit", writing two lines of text into the HTML document, returning the value in "celsius".

Table of Contents

 About This 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

 Defining Your Own Functions

Defining Your Own Functions - Example

 Calling Your Own Functions - Example

 Passing Parameters by Value or by Reference

 Function Parameters Are Passed as Local Copies

 Function Parameters Are Passed as Local Copies - Example

 Global and Local Variables - Scope Rules

 Global Variables - Examples

 Local Variables - Examples

 Collision of Global and Local Variables - Examples

 "return" Statement and Return Value

 Web Browser Supporting JavaScript

 Server-Side and Client-Side Web Scripting

 Introduction to Objects

 Defining Your Own Object Types

 Inheritance of Properties and Methods through the Prototype Object Chain

 'jrunscript' - JavaScript Shell Command from JDK

 Using Functions as "Function" Objects

 Introduction to Built-in Object Types

 W3C's Document Object Model (DOM) Specifications

 References

 PDF Printing Version