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Errata
JavaScript: The Definitive Guide, 4th Edition
By
David Flanagan
Publisher
: O'Reilly
Pub Date
: November 2001
ISBN
: 0-596-00048-0
Pages
: 936
Slots
: 1
This fourth edition of the definitive reference to
JavaScript, a scripting language that can be embedded
directly in web pages, covers the latest version of the
language, JavaScript 1.5, as supported by Netscape 6 and
Internet Explorer 6. The book also provides complete
coverage of the W3C DOM standard (Level 1 and Level 2),
while retaining material on the legacy Level 0 DOM for
backward compatibility.
Availability
JavaScript 1.5; JScript 5.5; ECMAScript v3
Synopsis
undefinedDescription
undefined is a global property that holds the
JavaScript undefined value. This is the same value
that is returned when you attempt to read the value of a nonexistent
object property. The undefined property is not
enumerated by for/in loops and cannot be deleted
with the delete operator. Note that
undefined is not a constant and can be set to any
other value, something that you should take care not to do.
When testing a value to see whether it is undefined, use the
=== operator, because the ==
operator treats the undefined value as equal to
null.
