how to use InstallVersion

[MacTan]

Hi,

    I hava a js file that checks for the installed version on the machine
and then decide whether to install or not. But the problem is how to the
string comparsion. According to the xpinstall doc, I can do something like

var vi = new InstallVersion();
mrscNew =  vi.init(mrscVerMajor, mrscVerMinor, mrscVerRelease,
mrscVerBuild);
mrscExistingVer = InstallTrigger.getVersion(mrscPluginPath);
if(mrscExistingVer.compareTo(mrscNewVer) < 0 )
    Install()


InstallTrigger is working.
But the InstallVersion() always return js script error.
Any help.

Thanks