[node-red-node-ui-vega] Append Data into a Vega Chart

[yasithdev]

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

Proposed changes

In node-red charts, when new data is received, it automatically appends that to the chart.
However, in ui_vega, it requires sending a new vega spec (with the updated data) to achieve this.
This introduces a severe lag for a complex spec.

In this PR I added a new function to push just the data into a ui_vega node.
This enables adding new data without triggering a full redraw.

How I've done it (at this point) is by sending messages into the node in two forms: templates and data.
Initially, I wanted to differentiate between them using msg.topic, but for some reason, it showed up as undefined.
For now, I've hacked around it by checking if msg.payload.$schema is present in the payload.

Any design revisions would be appreciated!

Checklist

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

[yasithdev]

Hello all, any update on this? Please let me know if you suggest any modifications.

[dceejay]

@HiroyasuNishiyama - this looks ok to me - but you guys are the main creators and users of this. OK with you ?

[HiroyasuNishiyama]

Wouldn't this fix break the compatibility of existing code because $schema property is not mandatory?
May I suggest adding msg.command property for setting data structure for controlling Vega specification?

[HiroyasuNishiyama]

I'm very sorry. 　
I didn't realize that I had failed to send the review results.

[yasithdev]

That's a good idea. I'll test it out with a msg.command property and update the PR.