JavaScript Tutorials - Herong's Tutorial Examples

∟Defining and Calling Functions

∟Defining Your Own Functions

This section provides a quick description of how to define your own functions and some basic features of a JavaScript function.

Like many programming languages, JavaScript allows you to define your own functions. JavaScript uses the following syntax format to define a new function:

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

There are 4 areas you need to know in order to define a new function:

• Function Name - You should name your function so that you can call it later. "function_name" in the above syntax format.
• Parameter List - You should name parameters of the function if you want to refer to them by names. "parameter_1", "parameter_2", ... in the above syntax format.
• Function Body - The list of statements provided inside curly braces {} forms the function body. "statement_1", "statement_2", ... in the above syntax format.
• Return Value - You should use "return" statements in the function body to end the execution of the function and to return a return value to the calling statement.

A JavaScript function has the following basic features:

• Primitive parameters are passed by values.
• Object parameters are passed by references.
• Extra parameters can be passed into a function without list them in the function definition.
• Parameters can be accessed through a built-in array "arguments[]" in the function body.
• Functions can be called recursively.
• A function provides a scope boundary for its local variables.

A tutorial example will be given in the next section showing your how to define a new function.

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

►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