node-red-contrib-boolean-logic

Node-RED nodes to easily perform boolean logic.

The problem

Node-RED does not support multiple inputs on nodes, and it has been discussed at length in this thread. The TL;DR - as I understand it - is that the developers of NR argue that multiple inputs makes it too complex for users without a background in electrical engineering and that it is preferred users of NR instead use other means to create the desired logic (i.e. write Javascript in function-nodes).

A solution

I really needed a simple and reusable way to perform boolean logic on multiple topics without the need to write the same code over and over.

Could this be solved using a subflow? No, function-node within a subflow cannot be configured on an instance basis which is required as the logic must know how many inputs it is expecting when performing operations such as A || B or A && (B || C). Yes, that could be hard coded, but then it would not be reusable. Also, a subflow cannot use the status indicator which is a great help to the user.

What I came up with are the following nodes.

• BooleanLogic: Can perform AND, OR and XOR operations on msg.payload on any number of topics.
• Invert: Inverts the msg.payload, e.g. true -> false.
• Debug: A debug node that displays the status direcly in the editor, making it easier to see the boolean value at a specific point.

All nodes attempts to convert the incoming msg.payload to a boolean value according to these rules:

• Boolean values are taken as-is.
• For numbers, 0 evaluates to false, all other numbers evaluates to true.
• Strings are converted to numbers if they match the format of a decimal value, then the same rule as for numbers are applied. If it does not match, it evaluates to false. Also, the string “true” evaluates to true.

BooleanLogic

This node must be configured with the expected number of topics. It will not output a value until it has received the configured number of topics. Also, if it receives more than the configured number of topics it will reset (but not output a value) and wait until it once again sees the configured number of topics.

Example

Version history

• 0.0.1 First release
• 0.0.2
  • Changed status indicators from dot to rings for false-values.
  • Reworked the conversion of input values to be consistent between numbers and strings with numeric meaning.