Tips for resolving the TSLint error in Firestore related to the possibly undefined object

I've been working with Firestore using the code snippet provided in this link. However, I keep encountering an error that says Object is possibly 'undefined' when trying to access data.name. I'm confident that the document does contain a name field. Any suggestions on how I can resolve this issue?

// Monitoring changes to any `user` document.
exports.countNameChanges = functions.firestore
    .document('users/{userId}')
    .onUpdate((change, context) => {
      // Retrieve current and previous values
      const data = change.after.data();
      const previousData = change.before.data();

      // Proceed only if there's a change in name.
      // Crucial to prevent infinite loops.
      if (data.name == previousData.name) return null;

      // Get the current count of name changes
      let count = data.name_change_count;
      if (!count) {
        count = 0;
      }

      // Promise a set operation to update the count
      return change.after.ref.set({
        name_change_count: count + 1
      }, {merge: true});
    });

Answer №1

Upon examining the TypeScript definition of change.after.data(), it becomes evident that the data method is specified to return either undefined or an object. It is essential to acknowledge this possibility of returning undefined, thus requiring a preliminary check before accessing properties or methods in strict mode. Even if one is confident about the existence of the named property, caution should be exercised.

To navigate this scenario, there are two options: either refrain from using strict mode (a risky decision as it guards against potential errors) or validate the existence of both data and previousData before proceeding with their usage.

const data = change.after.data();
const previousData = change.before.data();
if (data && previousData) {
    // perform actions based on them
}

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