DocumentChange

class

A DocumentChange represents a change to the documents matching a query. It contains the document affected and the type of change that occurred.

Properties

doc

read-only

DocumentSnapshot

The document affected by this change.

Example 

let query = firestore.collection('col').where('foo', '==', 'bar');

let unsubscribe = query.onSnapshot(querySnapshot => {
  for (let change of querySnapshot.docChanges) {
    console.log(change.doc.data());
  }
});

// Remove this listener.
unsubscribe();

newIndex

read-only

number

The index of the changed document in the result set immediately after this DocumentChange (i.e. supposing that all prior DocumentChange objects and the current DocumentChange object have been applied). Is -1 for 'removed' events.

Example 

let query = firestore.collection('col').where('foo', '==', 'bar');
let docsArray = [];

let unsubscribe = query.onSnapshot(querySnapshot => {
  for (let change of querySnapshot.docChanges) {
    if (change.oldIndex !== -1) {
      docsArray.splice(change.oldIndex, 1);
    }
    if (change.newIndex !== -1) {
      docsArray.splice(change.newIndex, 0, change.doc);
    }
  }
});

// Remove this listener.
unsubscribe();

oldIndex

read-only

number

The index of the changed document in the result set immediately prior to this DocumentChange (i.e. supposing that all prior DocumentChange objects have been applied). Is -1 for 'added' events.

Example 

let query = firestore.collection('col').where('foo', '==', 'bar');
let docsArray = [];

let unsubscribe = query.onSnapshot(querySnapshot => {
  for (let change of querySnapshot.docChanges) {
    if (change.oldIndex !== -1) {
      docsArray.splice(change.oldIndex, 1);
    }
    if (change.newIndex !== -1) {
      docsArray.splice(change.newIndex, 0, change.doc);
    }
  }
});

// Remove this listener.
unsubscribe();

type

read-only

string

The type of change ('added', 'modified', or 'removed').

Example 

let query = firestore.collection('col').where('foo', '==', 'bar');
let docsArray = [];

let unsubscribe = query.onSnapshot(querySnapshot => {
  for (let change of querySnapshot.docChanges) {
    console.log(`Type of change is ${change.type}`);
  }
});

// Remove this listener.
unsubscribe();