Search code examples
javascriptnode-red

Get difference between last and previous number

I have this function which parse a value received on mqtt. The value is actually a timestamp send by an arduino and is number like 1234 , 1345 etc...

var parts = msg.payload.trim().split(/[ |]+/);
var update = parts[10];
msg.payload = update;
return msg;

What i want is actually instead last value (which is update variable in my case) is to get difference between last received value and previous one. Basically if I receive 1234 and then 1345, I want to remember 1234 and the value returned by function to be 1345 - 1234 = 111.

Thank you

Solution

  • If you want to store a value to compare to later you need to look at how to use context to store it.

    The context is normally an in memory store for named variables, but it is backed by an API that can be used to persist the context between restarts.