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:45:18 - error TS2532: Object is possibly 'undefined'.
45     const data = change.after.data();

This is the function:

export const archiveChat = functions.firestore
  .document("chats/{chatId}")
  .onUpdate(change => {
    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;
    }
  });

I'm just trying to deploy the function to test it. And already searched the web for similar problems, but couldn't find any other posts that match my problem.

Solution 1

With the release of TypeScript 3.7, optional chaining (the ? operator) is now officially available.

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

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

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

Run the following to install the latest stable release of TypeScript.

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();

---

Additional points:

If you are using optional chaining in the conditional if statements, you will still need to ensure that you are doing proper value/type equality checking.

The following will fail in strict TypeScript, as you are possibly comparing an undefined value with a number.

if (_?.childs?.length > 0) 

Instead, this is what you should be doing:

if (_?.childs && _.childs.length > 0) 

Solution 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();

Solution 3

For others facing a similar problem to mine, where you know a particular object property cannot be null, you can use the non-null assertion operator (!) after the item in question. This was my code:

  const naciStatus = dataToSend.naci?.statusNACI;
  if (typeof naciStatus != "undefined") {
    switch (naciStatus) {
      case "AP":
        dataToSend.naci.certificateStatus = "FALSE";
        break;
      case "AS":
      case "WR":
        dataToSend.naci.certificateStatus = "TRUE";
        break;
      default:
        dataToSend.naci.certificateStatus = "";
    }
  }

And because dataToSend.naci cannot be undefined in the switch statement, the code can be updated to include exclamation marks as follows:

  const naciStatus = dataToSend.naci?.statusNACI;
  if (typeof naciStatus != "undefined") {
    switch (naciStatus) {
      case "AP":
        dataToSend.naci!.certificateStatus = "FALSE";
        break;
      case "AS":
      case "WR":
        dataToSend.naci!.certificateStatus = "TRUE";
        break;
      default:
        dataToSend.naci!.certificateStatus = "";
    }
  }

Comments

[Constantin Beer]

If I do that I'll get following error: error TS7030: Not all code paths return a value. 44 .onUpdate((change, context) =>

[Doug Stevenson]

You'll now need to return something when that first if statement returns false.

[Constantin Beer]

Oh, for some reason I thought that the error related to the change and context objects. #ashamed Now it works, but my code looks very bad, because I had to add an if query for the data object as well and just added return null; in the else branches. Is there a cleaner way to implement it? #HugeDougFan

[Constantin Beer]

With const data = change!.after!.data() I get an error, but with const data = change.after!.data() it works. Thank you a lot. :)

[distante]

Ok, I will fix it on the answer too.

[TimewiseGamgee]

Had the issue for an array on an object even with optional chaining.

[TimewiseGamgee]

Unfortunately it's difficult to format code in comments but here it goes... I had to supply the undefined check because it would throw "Object is possibly Undefined": if (listingData && listingData.images) { image = listingData?.images[0]?.imageUrl; }

[wentjun]

I'm thinking, is images optional field here? Thats why it could be undefined? In that case, do you wanna try this? if (listingData?.images) { image = listingData?.images?.[0].imageUrl; }

[TheEhsanSarshar]

even with optional chaining I still have the error if (_?.childs?.length > 0)

[ADM-IT]

Is there any way to disable that check? I don't think it's useful in typescript at all. Update: Just add "strictNullChecks": false, to the tsconfig.json file.

[wentjun]

@Ehsansarshar apologies for the late response, but I have addressed your issue on my post in a recent update

[wentjun]

@ADM-IT you might disable it, but it is still beneficial to do strict null/type checks.

[ADM-IT]

@wentjuin In many cases it is not predictable, so you just have to put many question marks everywhere to remove those warnings even if it's never going to be null.

[Dentrax]

Tried ? but I got: Property 'baz' does not exist on type 'never'. for the statement: const foo = bar?.baz