State of Node-RED dashboard nodes

Dashboard
1

I have already often built my own mechanism to store the output from a dashboard node into a context variable and then read the current state elsewhere when I need it, but I wanted to verify this:

  • There is no way to have a change node or function node to retrieve the current state of a dashboard node (i.e. switch is on/off) unless that state was saved to a context variable upon an output from the dashboard node.
2

Remember that the Dashboard and Node-RED run in two completely different environments, often on different devices. The only link between them is a Socket.IO based websocket connection.

Also remember that a Dasboard might be open in multiple tabs/windows, possibly on multiple devices.

The way that Dashboard works is that any updates that a user makes in any instance of the Dashboard are sent to Node-RED. It is up to you to sort out where they have come from and what to do with them.

It wouldn't make sense to have Node-RED to reach out to try and get a value - which instance of the Dashboard would it get the value from? What if there were a hundred different values in different instances?

3

I always assumed that Node-Red itself knew the nodes current status. For instance imagine 1 switch node:

  1. User 1 connects to dashboard and sees switch in default position (say off)
  2. User 1 switches to on
  3. User 2 connects to dashboard and sees the switch in its current position (now on due to change made by user 1).
4

It does not need to be saved to context, but it needs to be stored somewhere. I use MQTT retained topics to save the state of switches etc and to restore them on node-red restart. Also it could be stored in nodes such as Join nodes.

5

Here is the situation, I am looking to address. I have 3 lights (Kathy, Mike, Overhead). I am using the multiswitch to control them with Overhead also having a separate switch. Ignore the charger switch.
image

When I get an update of Mike to on, then I want the multiswitch to go from off to Mike. This is easy. If however, Kathy is already on and an external input of Mike just turned on, then I need to move the switch from Kathy to both.
So without storing the state of the multiswitch in a context variable and then using the incoming new Mike on input plus the context variable, I can't distinguish between the 2 states.

I have done this before, but wanted to make sure that there wasn't a direct line to the current state without having to manage it myself.

6

Dashboard nodes may store the last value I think and may offer that as a cached value to new connections and will send updates to all connected clients.

7

Feed all the states into a Join node in key/value mode and then when any one of them changes the join node will output a message with all the current states in it so you can do what you want with the switch.

2 Likes
8

Very elegant solution to the specific case I am working on.

1 Like
9

The concept will work in very many situations. I virtually never use context for such issues.

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10

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