Firestore - Listen to specific field change?

Question

How can I listen to a specific field change with firestore js sdk ?

In the documentation, they only seem to show how to listen for the whole document, if any of the

Answer 1

As Doug mentioned above, the entire document will be received in your function. However, I have created a filter function, which I named field, just to ignore document changes when those happened in fields that I am not interested in.

You can copy and use the function field linked above in your code. Example:

export const yourCloudFunction = functions.firestore
.document('/your-path')
  .onUpdate(
    field('foo', 'REMOVED', (change, context) => {

      console.log('Will get here only if foo was removed');

    }),
  );

Important: The field function is not avoiding your function to be executed if changes happened in other fields, it will just ignore when the change is not what you want. If your document is too big, you should probably consider Doug's suggestion.