The Opera pitfall

Using the navigator object to screen for Opera (an emerging browser) is not so straightforward. Opera (Opera 6 specifically) purports to take on multiple identities in terms of what its navigator object returns. By default, Opera 6 is set to identify as IE5, meaning that when its navigator object is probed, it will return IE5's identity (changeable by the user through File->Quick Preferences). Most likely, the rationale for this is so that scripts originally intended for IE will also work in Opera 6.

Let's examine another navigator property of Opera 6:

navigator.userAgent

Depending on how Opera 6 is set to identify itself , here is what navigator.userAgent returns:

As IE: Mozil/4.0 (compatible; MSIE 5.0; Windows XP) Opera 6.0 [en]
As Moz5: Mozil/5.0 (Windows XP; U) Opera 6.0 [en]
As Moz4.76: Mozil/4.76 (Windows XP; U) Opera 6.0 [en]
As Moz3.0: Mozil/3.0 (Windows XP; U) Opera 6.0 [en]
As Opera: Ope/6.0 (Windows XP; U) [en]

Consequently, the expression

if (navigator.userAgent.indexOf("Opera 6")!=-1)

will fail if the user has his or her browser set to identify as Opera.

Here is the JavaScript code needed to detect Opera 6:

if ((navigator.userAgent.indexOf("Opera 6")!=-1) ||(navigator.userAgent.indexOf("Ope/6")!=-1))