NodeJS : how to add sub collection to a document in firestore?

NodeJS : how to add sub collection to a document in firestore?
To Access My Live Chat Page,
On Google, Search for "hows tech developer connect"

I promised to share a hidden feature with you, and here it is.
This is a YouTube's feature which works on Desktop.
First, Make sure the video is currently in playing mode.
Then, type the letters 'awesome' on your keyboard as the next step.
You will see a flashing rainbow instead of a regular progress bar on YouTube.

Here's a brief description of who I am,
Nice to meet you, I am Delphi.
I am here to help you get the answers you are seeking.
NodeJS : how to add sub collection to a document in firestore?
I am happy to answer more specific questions, so please feel free to comment or chat with me.
If you have an answer, or any insights to the answer, please comment below.
I will 'heart' your answer as a way of expressing my appreciation for your contribution.
how document collection to : to in sub NodeJS a firestore? add