Finding java once and for all - no batch file nonsense

findjava.js

getJRE = function(ver, wantJDK) {
	var wshShell = new ActiveXObject("WScript.Shell");
	var key = "HKLM\\SOFTWARE\\JavaSoft\\" + 
		(wantJDK ? "Java Development Kit\\" : "Java Runtime Environment\\") +
		ver +
		"\\JavaHome";
	//WScript.Echo(key);
	try {
		return wshShell.RegRead(key)
	} catch(e) {
		return "";
	} 
}

getCurrentVersion = function() {
	var wshShell = new ActiveXObject("WScript.Shell");
	try {
		return wshShell.RegRead("HKLM\\SOFTWARE\\JavaSoft\\Java Runtime Environment\\CurrentVersion");
	} catch(e) {
		return "";
	}
}
//WScript.Echo(getCurrentVersion());
versions = [
	getCurrentVersion(),
	"1.7",
	"1.6",
	"1.5"
];

buildCandidates = function(jdkRequired) {
	var ret = [];
	for (ver in versions) {
		var jdk = getJRE(versions[ver], true);
		if (jdk != "") {
			ret.push(jdk);
		}
		if (!jdkRequired) {
			var jre = getJRE(versions[ver], false);
			if (jre != "") {
				ret.push(jre);
			}
		}
	}
	return ret;
}

makeFileChecker = function(path) {
	return function(root) {
		var fso = new ActiveXObject("Scripting.FileSystemObject");
		if (fso.FileExists(fso.BuildPath(root, path))) {
			return true;
		} else {
			return false;
		}
	}
}


if (!Array.prototype.filter)
{
  Array.prototype.filter = function(fun /*, thisp*/)
  {
    var len = this.length;
    if (typeof fun != "function")
      throw new TypeError();

    var res = new Array();
    var thisp = arguments[1];
    for (var i = 0; i < len; i++)
    {
      if (i in this)
      {
        var val = this[i]; // in case fun mutates this
        if (fun.call(thisp, val, i, this))
          res.push(val);
      }
    }

    return res;
  };
}
if (!Array.prototype.map)
{
  Array.prototype.map = function(fun /*, thisp*/)
  {
    var len = this.length;
    if (typeof fun != "function")
      throw new TypeError();

    var res = new Array(len);
    var thisp = arguments[1];
    for (var i = 0; i < len; i++)
    {
      if (i in this)
        res[i] = fun.call(thisp, this[i], i, this);
    }

    return res;
  };
}
hasJavaExe = makeFileChecker("bin\\java.exe");
hasClientJVMDLL = makeFileChecker("bin\\client\\jvm.dll");
hasServerJVMDLL = makeFileChecker("bin\\server\\jvm.dll");
isSuitable = function(root) {
	return hasJavaExe(root) && ( hasClientJVMDLL(root) || hasServerJVMDLL(root) );
}

justJavaExeDir = function(root) {
	var fso = new ActiveXObject("Scripting.FileSystemObject");
	return fso.BuildPath(root, "bin");
}

jvmDLLAndJavaExeDir = function(root) {
	var fso = new ActiveXObject("Scripting.FileSystemObject");
	return justJavaExeDir(root) + ";" +
		(hasClientJVMDLL(root) ?
			fso.BuildPath(root, "bin\\client") :
			fso.BuildPath(root, "bin\\server")
		);
}

//WScript.Echo("Starting");
locs = buildCandidates(false);
JAVA_PATH=locs.filter(hasJavaExe).map(justJavaExeDir).join(";");
JAVA_JNI_PATH=locs.filter(isSuitable).map(jvmDLLAndJavaExeDir).join(";");
//WScript.Echo("done");

launchCmdPrompt = function(cmd) {
	var wshShell = new ActiveXObject("WScript.Shell");
	wshShell.Run("%COMSPEC% /k " + cmd);
}

chdir = function(abspath) {
	var wshShell = new ActiveXObject("WScript.Shell");
	wshShell.CurrentDirectory = abspath;
}

chdirIfPossible = function(dir) {
	var fso = new ActiveXObject("Scripting.FileSystemObject");
	if (fso.FolderExists(dir)) {
		 chdir(fso.GetAbsolutePathName(dir));
		 return true;
	}
	return false;
}
var wshShell = new ActiveXObject("WScript.Shell");
var wshProcEnv = wshShell.Environment("PROCESS");

wshProcEnv("PATH") = JAVA_JNI_PATH + wshProcEnv("PATH");

if (WScript.Arguments.length == 1) {
	var didChdir = chdirIfPossible(WScript.Arguments.Item(0));
	if (didChdir) {
		launchCmdPrompt("echo In Java/JNI command prompt in your desired directory.");
		WScript.Quit();
	} else {
		// todo run program here.
	}
}

launchCmdPrompt("echo In Java/JNI command prompt.");