This article was written and submitted by an external developer. The Google Desktop Team thanks Benjamin Schirmer for his time and expertise.
Although system information
is available through the framework.system object, you sometimes need
more than it can offer.
Another way is to use
a hybrid dll, but this is usually a lot of work. This article will
show you how to write custom JavaScript objects that retrieve system
information using the Windows Management Information (WMI) classes.
The custom object in this article will request operating system information, which can be used to determine the operating system installed on the user's machine. This is very useful if your gadget can only run under a certain operating system, or you can use it to select between OS specific hybrid DLLs you have written.
In the end, we want to be able to use a simple object that gathers operating system information. For example, it should be able to easily detect Windows Vista:
var os = new OS();
if (os.isVista()) {
doSomething();
}
The first thing you need to know is how to call a specific WMI
class in JavaScript. Every call to WMI starts with winmgmts:.
We will use an impersonationLevel of Impersonate,
which will allow us to request all information the current user has
access to. After the optional impersonationLevel, what follows is the
identification of the computer we want to request information about.
To use the current computer, you just use \\.. For other
computers, you can use \\hostname. At the end we will add
the namespace of our call, which is the standard \root\cimv2
namespace. Your final call should look like this:
winmgmts:{impersonationLevel=Impersonate}\\.\root\cimv2
To use this WMI string to access the information, you must acquire
the WMI object using the JavaScript GetObject function.
The returned object will provide an ExecQuery method, which allows you
to execute queries to the Windows Management Information Interface.
var wmi = GetObject("winmgmts:{impersonationLevel=Impersonate}\\\\.\\root\\cimv2");
var query = "Select * From Win32_OperatingSystem";
e = new Enumerator(wmi.ExecQuery(query));
var data = e.item();
The code above will request a WMI object and all
information from the Win32_OperatingSystem class. You can use
Enumerator to iterate through all the different results. In our
example, we just need the first result. This class has all the
information we need to identify the operating system of the user.
For additional information, please check out
http://msdn2.microsoft.com/en-us/library/aa392727.aspx,
which provides a complete list of all WMI classes.
Here are some more WMI classes that can be used for performance monitoring. Please note that some classes require a parameter as input.
Select * from Win32_PerfRawData_PerfDisk_LogicalDisk Where Name = 'C:'
Select * From Win32_PerfRawData_PerfOS_Processor Where Name = '0'
will retrieve the processor information for the first processor. You can retrieve
the number of processors using Win32_ComputerSystem.
We could use the data variable above to access the
different attributes, but it is not very practical since we would
have to repeat the query call to WMI whenever we wanted some particular attribute. The easiest way is to create a custom object that
provides access to the diffferent attributes, and even additional
methods for working with the data.
To create the new object, we first have to
create a constructor. This is basically a function that is
executed when our object is created with the new
call. The constructor executes the code to retrieve the desired
information and fills the attributes of the object.
function OS() {
var wmi = GetObject("winmgmts:{impersonationLevel=Impersonate}\\\\.\\root\\cimv2");
var query = "Select * From Win32_OperatingSystem";
e = new Enumerator(wmi.ExecQuery(query));
var data = e.item();
this.windowsSKU = data.OpertingSystemSKU;
this.serial = data.SerialNumber;
this.build = data.BuildNumber;
this.buildType = data.BuildType;
this.servicePackMajor = data.ServicePackMajorVersion;
this.servicePackMinor = data.ServicePackMinorVersion;
this.version = data.Version;
this.caption = data.Caption;
this.name = data.Name;
this.name = this.name.substring(0, this.name.indexOf("|")-1)
}
Our new object OS now provides several
attributes, like version and name
of the operating system; but we're not
finished just yet. We will add some methods to the object to
provide additional functionality. In the beginning of this article, I
mentioned the isVista method which should tell us if we are running on a
Vista machine. This method will use a custom compareVersion
method to compare the version of the current
operating system to the Vista version string.
OS.prototype.compareVersion = function(version2) {
var v1 = this.version.split(".");
var v2 = version2.split(".");
var result = 0;
for (var i=0; i<v1.length; i++) {
if (v1[i] > v2[i]) {
result = 1;
}
else if (v1[i] < v2[i]) {
result = -1;
}
if (result != 0) {
break;
}
}
if (v2.length > v1.length && v2[v2.length-1] != 0) {
result = -1;
}
return (result == 0);
}
OS.prototype.isVista = function() {
return this.compareVersion("6.0");
}
If you want, you can extend the object with more of these methods.
If you want an isXP method to check for Windows XP, you could simply
add:
OS.prototype.isXP = function() {
return this.compareVersion("5.1");
}
Our custom object is now finished. The best way to make it reusable is to save the code for this object into a separate JavaScript file, for example oshelper.js. If you need the object in a new gadget, simply copy the file to the new project and add it to your xml file. Now that's code reusability!
To use the object in your code, you must create a new
OS object and
then call the method or attributes you need.
var os = new OS();
if (os.isVista()) {
alert("You are running:\n"+os.name);
doSomething();
}
Custom objects are a great way to create reusable code, and WMI is a very powerful way to retrieve system information. Together they make a perfect team. So the next time when you need some information that is not available in the framework, you might want to check if a WMI will provide the information you need.
Be sure to try out the Operating System Gadget to see a gadget that uses the custom object from this article.
Benjamin Schirmer holds a diploma in engineering from Albstadt-Sigmaringen University and is an enthusiastic gadget programmer. He loves to explore new technologies. In his spare time, he likes watching movies, TV series, and going out with his friends. In the future, he wants to be a Googler himself. You can visit his gadgets page for a list of all his cool Google Desktop gadgets.
This work is licensed under a
Creative Commons Attribution-Share Alike 3.0 United States License.