Local Variables - Examples

JavaScript Tutorials - Herong's Tutorial Examples

∟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) 2008 HerongYang.com. All Rights Reserved.
-->
<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