1)var url = "/XMII/Runner?Transaction=" + currTrxFullPath + "&OutputParameter=*";
Keep the url variable as it is.. no change. "/XMII..." would automatically pickup you workbench's server and host name.
2)var currTrxFullPath = "Default/Transactions/HelloWorld_Runner_Output"; // Full Path of the transaction
This is the path of the transaction. If your transaction is in "Project1" under "Folder1". Then the path would be Project1/Folder1/TransactionName.
You could also get the path from the workbench. Open the transaction, on the left bottom panel, there are three tabs. The third one (forgot the name 
) will have the path of the transaction. Place the path in the currTrxFullPath variable.
The reason of not getting the output is because of wrong transaction path.
For the example to work,
1. Your transaction should contain, 2 input parameters of type integer. Name them "one" and "two" . So create two transaction properties
2. Your transaction should contain 1 Output parameter of type interger. Name it "Out". Create a transaction property for this and select the Output parameter flag.
3. Your transaction should contain an Assignment action block.
In the assignment action block, Target should be "Out", expression should be Transaction.one + Transaction.two . In short, create a expression to add two input parameters and assign in to the output. It should do.