Accessing Array Elements with Indexes

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

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