How can I solve the error 'TS2532: Object is possibly 'undefined'?

Question

I\'m trying to rebuild a web app example that uses Firebase Cloud Functions and Firestore. When deploying a function I get the following error:

src/index.ts         


        

Answer 1

As of October 2019, optional chaining (the ? operator) is now available on TypeScript 3.7 (Beta). You may install that version by running the following command:

npm install typescript@beta

As such, you can simplify your expression to the following:

const data = change?.after?.data();

You may read more about it from the release notes, which cover other interesting features released on that version.

Update (as of November 2019)

TypeScript's optional chaining is now officially available. Installing the latest version of typescript should allow you to access the cool new features.

npm install typescript

That being said, Optional Chaining can be used alongside Nullish Coalescing to provide a fallback value when dealing with null or undefined values

const data = change?.after?.data() ?? someOtherData();

Answer 2

Edit / Update:

If you are using Typescript 3.7 or newer you can now also do:

    const data = change?.after?.data();

    if(!data) {
      console.error('No data here!');
       return null
    }

    const maxLen = 100;
    const msgLen = data.messages.length;
    const charLen = JSON.stringify(data).length;

    const batch = db.batch();

    if (charLen >= 10000 || msgLen >= maxLen) {

      // Always delete at least 1 message
      const deleteCount = msgLen - maxLen <= 0 ? 1 : msgLen - maxLen
      data.messages.splice(0, deleteCount);

      const ref = db.collection("chats").doc(change.after.id);

      batch.set(ref, data, { merge: true });

      return batch.commit();
    } else {
      return null;
    }

Original Response

Typescript is saying that change or data is possibly undefined (depending on what onUpdate returns).

So you should wrap it in a null/undefined check:

if(change && change.after && change.after.data){
    const data = change.after.data();

    const maxLen = 100;
    const msgLen = data.messages.length;
    const charLen = JSON.stringify(data).length;

    const batch = db.batch();

    if (charLen >= 10000 || msgLen >= maxLen) {

      // Always delete at least 1 message
      const deleteCount = msgLen - maxLen <= 0 ? 1 : msgLen - maxLen
      data.messages.splice(0, deleteCount);

      const ref = db.collection("chats").doc(change.after.id);

      batch.set(ref, data, { merge: true });

      return batch.commit();
    } else {
      return null;
    }
}

If you are 100% sure that your object is always defined then you can put this:

const data = change.after!.data();