Firebase Cloud Functions Object possibly 'undefined'

Question

I have the following code in typescript and i get this error on the line: change.after.data();, Object is posibbly 'undefined':

import * as functions from 'firebase-functions'
import * as admin from 'firebase-admin'

admin.initializeApp()

export const onEditModeUpdate = 
functions.firestore.document("Settings/ShiftsEditMode").onUpdate(change=> {
    const after = change.after.data();
    const payload = {
        data: {
            temp: String(after.temp),
            conditions: after.conditions
        }
    }
    return admin.messaging().sendToTopic("Settings/ShiftsEditMode", payload)
})

what I want to do is to send to my app a notification whenever something in firestore changes, I followed the official documentation but I get the error, I think this has to do with node.js version. Any help, please?

Object is possibly 'undefined'.ts(2532)

Erjon
– Erjon

2019-03-14 16:13:03 +00:00
Commented Mar 14, 2019 at 16:13 — Erjon
– Erjon, Commented Mar 14, 2019 at 16:13

Doug Stevenson · Accepted Answer · 2019-03-14 16:24:21Z

3

Your change parameter is of type Change. If you click through to it in VSCode, you'll see it's definition here:

export declare class Change<T> {
    before?: T;
    after?: T;
    constructor(before?: T, after?: T);
}

Notice that its before and after properties are both optional, marked with a ? in the type. This means that it's possible that the values are undefined.

It's likely that your TypeScript config in tsconfig.json contains a line for "strict": true, which tells TypeScript not warn you whenever you try to access a property that could be undefined without explicitly checking it first. That's the error you're seeing here.

You have two options:

1) Remove that line from your tsconfig.json

2) Or check to see if it's defined first

if (change.after) {
    const after = change.after.data();
    const payload = {
        data: {
            temp: String(after.temp),
            conditions: after.conditions
        }
    }
    return admin.messaging().sendToTopic("Settings/ShiftsEditMode", payload)
}
else {
    return null;
}

answered Mar 14, 2019 at 16:24

Doug Stevenson

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4 Comments

Erjon Over a year ago

Thank you very much, I was following your tutorial in a social network. Thanks again it did the trick :)

Doug Stevenson Over a year ago

The default addition of strict: true is pretty recent for projects created with the Firebase CLI, and my tutorials actually don't use that. So it's kind of a bummer that today's defaults no longer match the tutorials.

Erjon Over a year ago

Another thing if it is possible, i get this error in function logs when i change the data: Messaging payload contains an invalid value for the "data.conditions" property. Values must be strings.

Doug Stevenson Over a year ago

That sounds like a completely different thing. Please post a separate question about that one.

Richard · Accepted Answer · 2019-03-14 16:22:36Z

2

If you look at the types for the onUpdate handler, the argument for change has 2 optional properties, after and before:

class Change<T> {
    before?: T;
    after?: T;
    constructor(before?: T, after?: T);
}

Because you want to access after, you'll need to wrap it in a conditional, something like this following:

functions.firestore.document("Settings/ShiftsEditMode").onUpdate(change=> {
    if (change.after) {
        const after = change.after.data();
        ...
    }
}

answered Mar 14, 2019 at 16:22

Richard

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