Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

As discussed on discourse: https://discourse.nodered.org/t/defining-utility-functions-for-re-use-in-a-function-node/100294)

A way of generating re-usable logic that a function node can call without leaving the function execution environment.

Simplifying logic reuse is a commonly requested feature. This PR provides a means that fits with the flow based paradigm in that it permits calling re-usable logic in a function node but also utilises the well established subroutines visual flow using link-in ~ link-out nodes to build the re-usable logic.

Example

const returnMsg = await node.linkcall('nested-1', msg, { timeout: 1000 })
return returnMsg;

In the PR

• Added node.linkcall to the function node vm
  • linkcall(target: string, msg: object, options?: { timeout?: number; clone?: boolean; [key: string]: any }): Promise<object>;
• Some logic from link nodes was refactored to common runtime code
• Example flows were updated to demonstrate functionality

Tests added:

link call from function
      ✔ should call subroutine on same tab by name and get response
      ✔ should call subroutine on different tab by name and get response
      ✔ should call subroutine on same tab by node id and get response
      ✔ should call subroutine on different tab by node id and get response
      ✔ should call subroutine on same tab even when there are same named targets on other tabs
      ✔ should call nested subroutines
      ✔ should timeout waiting for link return (507ms)
      ✔ should raise error for non-existent target subroutine
      ✔ should raise error due to multiple targets on same tab
      ✔ should raise error due to multiple targets on different tabs

Demo flows for trying out the PR

I will attached demo flows in follow up

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run npm run test to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality