Local Variables - Examples

This section provides a tutorial example on how local variables behave inside and outside functions.

To see how local variables behave inside and outside functions, I wrote the following tutorial example:

<html>
<!-- Local_Variable_Scope.html
   Copyright (c) 2013 by Dr. Herong Yang, herongyang.com
-->
<head><title>Local Variable Scope</title></head>
<body>
<pre>
<script type="text/javascript">

   scopeCheck();

   document.write("\n\nAfter function call:");
   
   // localVar is not a valid variable
   // document.write("\n   localVar = " + localVar);
   document.write("\n   localVar is not valid");

   // localNoVar is a valid variable, auto-declared by scopeCheck()
   document.write("\n   localNoVar = " + localNoVar);

function scopeCheck() {
   var localVar;
   localVar = "Apple";
   localNoVar = "Orange";

   localVar = localVar + " - Updated";
   localNoVar = localNoVar + " - Updated";

   document.write("\n\nUpdated value in function:");
   document.write("\n   localVar = " + localVar);
   document.write("\n   localNoVar = " + localNoVar);
}
</script>
</pre>
</body>
</html>

This tutorial example tests two "local" variables: one declared with a "var" statement, and one without. They behave differently. "localVar" declared with a "var" statement is a true local variable. "localNoVar" auto-declared without a "var" statement becomes a global variable. See the output:

Updated value in function:
   localVar = Apple - Updated
   localNoVar = Orange - Updated

After function call:
   localVar is not valid
   localNoVar = Orange - Updated

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