JavaScript Tutorials - Herong's Tutorial Examples

∟Creating, Accessing, and Manipulating Arrays

∟Accessing Array Elements with Indexes

This section provides a tutorial example on how to access array elements with element indexes.

Array elements can be access with array indexes with several simple rules:

• Like many other programming languages, an array element can be accessed with the array element syntax of array_name[index].
• An array index starts with 0.
• The length of an array is defined as the highest index of all elements plus 1.
• There is no index-out-of-bound exception in JavaScript.
• If an index greater than the array length is specified when retrieving an array element, the "undefined" value will be returned.
• If an index greater than the array length is specified when storing an array element, the array will be expanded to store the element at the specified index.

Here is a tutorial example JavaScript that shows you how to store or retrieve array elements with element indexes:

<html>
<!-- Access_Array_Elements.html
   Copyright (c) 2002 HerongYang.com. All Rights Reserved.
-->
<head><title>Access Array Elements</title></head>
<body>
<pre>
<script type="text/javascript">

   // Creating an empty array
   var glossary = new Array();

   // Adding the first element
   glossary[0] = "JavaScript";

   // Adding the second element at index 10
   // This extends the array length to 11
   glossary[10] = "Web";

   document.write("Element at index of 0: "+glossary[0]+"\n");
   document.write("Element at index of 5: "+glossary[5]+"\n");
   document.write("Element at index of 10: "+glossary[10]+"\n");
   document.write("Element at index of 15: "+glossary[15]+"\n");
</script>
</pre>
</body>
</html>

The output of this sample JavaScript is:

Element at index of 0: JavaScript
Element at index of 5: undefined
Element at index of 10: Web
Element at index of 15: undefined

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

 What Is an Array

 Creating an Array Object

►Accessing Array Elements with Indexes

 Truncating and Iterating Array Elements

 Array Object Instance Methods

 Array Object Instance Method Examples

 Defining and Calling Functions

 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

 AJAX (Asynchronous JavaScript And XML)

 References

 Full Version in PDF/EPUB

Accessing Array Elements with Indexes - Updated in 2023, by Herong Yang