Language Java Script Definitive Examples 13.1.TXT

 <!-- This example is from the book _JavaScript: The Definitive Guide_.     -->
<!-- Written by David Flanagan.  Copyright (c) 1996 O'Reilly & Associates. -->
<!-- This example is provided WITHOUT WARRANTY either expressed or implied.-->
<!-- You may study, use, modify, and distribute it for any purpose.        -->
<SCRIPT>
// Return the version number times 1000.  This means that version 
// 2.02 would yield 2020, and version 3.0 would yield 3000.
// We multiply because Navigator versions 2.0x convert numbers like
// 2.02 to strings like "2.0199999999875"
function _get_version()
{
    return Math.round(parseFloat(navigator.appVersion) * 1000);
}

// Figure out the OS we are running on, based on the appVersion property
function _get_os()
{
    if (navigator.appVersion.indexOf("Win95") > 0) return "WIN95";
    else if (navigator.appVersion.indexOf("Win16") > 0) return "WIN31";
    else if (navigator.appVersion.indexOf("Mac") > 0) return "MAC";
    else if (navigator.appVersion.indexOf("X11") > 0) return "UNIX";
    else return "UNKNOWN";
}

// Create the object we'll use to store the version information.
var browser =index.html new Object();

// First, check if it is a Netscape browser.
if (navigator.appName.substring(0,8) == "Netscape") { 
    // if so, set the name variable appropriately
    browser.name =  "NN";
    // then parse navigator.appVersion to figure out what version
    browser.version = _get_version();
    // Then use appVersion again to determine the OS.
    browser.os = _get_os();
}

// Otherwise, see if it is a Microsoft browser.
//
// If so, we set all the variables directly, because MSIE only has
// one JavaScript-enabled version, and it only runs on one platform.
// We don't use Navigator.appVersion to compute the version number, because
// it returns a Netscape-compatible value of 2.0 rather than the true
// MSIE version number 3.0.  We don't use it to compute the OS, because
// MSIE encodes that information with different strings than Navigator
// does, so we can't use the _get_os() function above.
// 
// This code will have to be updated when a new version of MSIE is released
// but we'll have to wait and see how MS encodes the information in the
// various Navigator object properties we can update the code.
else if (navigator.appName.substring(0,9) == "Microsoft") {
    browser.name = "MSIE";
    browser.version = 3000;
    browser.os = "WIN95";
}

// Otherwise, it is some unknown browser that supports JavaScript.
// So we try to guess the browser name, version number and os, assuming
// that this browser stores the information in the same format as Navigator.
else { 
    browser.name = navigator.appName;
    browser.version = _get_version();
    browser.os = _get_os();
}

// Now figure out what version of JavaScript is supported by the browser.
// Start by assuming that only version 1.0 is supported.
browser.langlevel = 1000;
</SCRIPT>

<SCRIPT LANGUAGE="JavaScript1.1">
// if the browser supports JavaScript 1.1, update the langlevel variable
browser.langlevel =index.html 1100;
</SCRIPT>

<SCRIPT LANGUAGE="JavaScript1.2">
// if the browser supports JavaScript 1.2, update the langlevel variable
browser.langlevel =index.html 1200;
</SCRIPT>

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