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To verify if a Firestore document contains a specific field, you can use the .get() method to retrieve the document and then use the .exists property of the returned DocumentSnapshot to check if the field exists.

For example, if you want to check if a document with an ID of "myDoc" in a collection called "myCollection" contains a field called "myField", you can use the following code in JavaScript:

const docRef = db.collection("myCollection").doc("myDoc");

docRef.get().then(doc => {
  if (doc.exists && doc.data().hasOwnProperty("myField")) {
    console.log("The document contains the field 'myField'");
  } else {
    console.log("The document does not contain the field 'myField'");
  }
});

In this code, the .exist property checks if the document exists in the first place and then .hasOwnProperty("myField") is used to check if the document contains the field.