DocumentChange
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
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
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
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
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();