Download UltraDMM , add two ut61e meters in "Manage meters" window, each with its own serial port.
Connect to both meters, open Tools > Meter log and wait for the software to log all the information then you can export the data for each meter to xml or csv
Then you can import the csv files into your application and plot whatever you want.
I don't see any way for ultradmm to dump to disk the records as they are read, so I'm not sure you can do it in realtime as you get data from meter.
The protocol for the UT61E is well documented, you could in theory get the raw bytes from the serial port and decode them yourself. It's not hard. I'm just not sure how you'd connect to serial using Javascript.