Qlik Sense: fail-and-retry connection sample script

When connecting to a data connection, developer may want to setup fail-and-retry logic. When main connection fails, backup connection is used.
How to achieve it?

Setting errormode to 0 can force script continue after a failure.

The code will look like this:
========================================================
//Suppress reload failure in case of connection failure
Set errormode = 0;
//Connect to the main Connection
LIB CONNECT TO 'MainConnection';
//Evaluate error code
LET tempErrorDetails = ScriptErrorDetails;
IF Len(tempErrorDetails) > 0 THEN
    // If there is an error connecting to this connection
   trace ERROR: $(tempErrorDetails);
   LIB CONNECT TO 'backupConnection';
End If

//Resume error mode
Set errormode = 1;
// Load Script Start

// Load Script End

// Disconnect
DisConnect;
========================================================

Sample QVF is also attached. Please modify the sample code in it accordingly before using.