Transforming TypeScript snapshot data in Firebase Cloud Functions into a string format for notification purposes

Question

Transforming TypeScript snapshot data in Firebase Cloud Functions into a string format for notification purposes

I've encountered the following code for cloud functions, which is intended to send a notification to the user upon the creation of a new follower. However, I'm facing an issue regarding converting the snap into a string in order to address the error message provided below.

 function sendNewFollowNotificationFunc(uuid: string, newFollower: string) {
  // const userRef = admin.database().ref('PeopleWhoFollowMe').child(uuid)
  // const fetchAndUpdate = userRef.once('value')
  console.log('User to send notification', uuid);

  admin.database().ref(`UsersFireTokens`).child(uuid).child("token").once('value')
  .then(snap => {
    const token = snap.val//I dont know how, from here I should be handling this inorder to get the value at this location which is the token
    // This registration token comes from the client FCM SDKs.
    var registrationToken = token;

    var message = {
      data: {
        text: 'This is a test',
        time: '2:45'
      },
      token: registrationToken
    };

    // Send a message to the device corresponding to the provided
    // registration token.
    admin.messaging().send(message)//error here
      .then((response) => {
        // Response is a message ID string.
        console.log('Successfully sent message:', response);
      })
      .catch((error) => {
        console.log('Error sending message:', error);
      });
  })
  .catch(error => {
    console.log("Error in catch: "+error)
    response.status(500).send(error)
  })

Several errors are occurring, such as:

Argument of type '{ data: { text: string; time: string; }; token: string | null; }' is not assignable to parameter of type 'Message'. Type '{ data: { text: string; time: string; }; token: string | null; }' is not assignable to type 'TokenMessage'. Types of property 'token' are incompatible. Type 'string | null' is not assignable to type 'string'. Type 'null' is not assignable to type 'string'.ts(2345)

What am I doing wrong and how can I fix it?

Update:

This is my code:

function sendNewFollowNotificationFunc(uuid: string, newFollower: string) {
  // const userRef = admin.database().ref('PeopleWhoFollowMe').child(uuid)
  // const fetchAndUpdate = userRef.once('value')
  console.log('User to send notification', uuid);

  admin.database().ref(`UsersFireTokens`).child(uuid).child("token").once('value')
  .then(snap => {
    //What should I be doing here and how?
console.log('token value', snap.val);//doing this returns a strange function thing in the logs

  })
  .catch(error => {
    console.log("Error in catch: "+error)
    response.status(500).send(error)
  })
}

typescript firebase firebase-cloud-messaging google-cloud-functions

Answer 1

Answer №1

The complex and lengthy tsc message indicates that the type of your message variable is:

{ data: { text: string; time: string; }; token: string | null; }

however, the send function requires a TokenMessage. It is not possible to fully understand the structure of the TokenMessage from your code alone, but it seems to include a token field of type string. On the other hand, your message has a token field with type string | null. This mismatch in types suggests that your message may lack a token, whereas the send function expects a value with an assured token string.

What am I doing wrong and how can I fix it?

You need to ensure that when calling send, the provided value aligns with the TokenMessage type.

One approach is to cast the message to TokenMessage:

 admin.messaging().send(message as Message)

(tldr: using the above line will likely resolve your issue)

In some cases, two types are too incompatible for casting. In such scenarios, forcing a conversion as shown above may not work. Instead, you could first cast to any and then to the desired type:

admin.messaging().send(message as any as Message)

That being said, this may not always be the recommended course of action:

If TypeScript raises concerns about message potentially lacking a token, it's useful. Typically, you can address these tsc warnings by asserting over your variables:

function getToken(): string | null {
    return 'f00';
}

function test(s: string) { 

}

const t = getToken();

test(t); // error

if (t) {
    test(t); // no error, considered safe
    // this practice ensures handling of potential null values during development
}

However, this method doesn't seem applicable to object fields:

function getToken(): string | null {
    return 'f00';
}

interface Message{
    token: string;
}

function send(m: Message) { 

}

const t = getToken();

const message = {
    token: t,
}

send(message); // error

if (t) {
    send(message); // error
}

if (message.token) { 
    send(message); // still an error, which is perplexing. At this point, tsc should recognize that message meets the requirements of Message. There appears to be a confusion here.
}

send(message as Message); // valid

In general, it is advisable and safer to handle null checks through if statements rather than manual type casting. However, there can be instances where alternative options are limited.

Answer 2

The complex and lengthy tsc message indicates that the type of your message variable is:

{ data: { text: string; time: string; }; token: string | null; }

however, the send function requires a TokenMessage. It is not possible to fully understand the structure of the TokenMessage from your code alone, but it seems to include a token field of type string. On the other hand, your message has a token field with type string | null. This mismatch in types suggests that your message may lack a token, whereas the send function expects a value with an assured token string.

What am I doing wrong and how can I fix it?

You need to ensure that when calling send, the provided value aligns with the TokenMessage type.

One approach is to cast the message to TokenMessage:

 admin.messaging().send(message as Message)

(tldr: using the above line will likely resolve your issue)

In some cases, two types are too incompatible for casting. In such scenarios, forcing a conversion as shown above may not work. Instead, you could first cast to any and then to the desired type:

admin.messaging().send(message as any as Message)

That being said, this may not always be the recommended course of action:

If TypeScript raises concerns about message potentially lacking a token, it's useful. Typically, you can address these tsc warnings by asserting over your variables:

function getToken(): string | null {
    return 'f00';
}

function test(s: string) { 

}

const t = getToken();

test(t); // error

if (t) {
    test(t); // no error, considered safe
    // this practice ensures handling of potential null values during development
}

However, this method doesn't seem applicable to object fields:

function getToken(): string | null {
    return 'f00';
}

interface Message{
    token: string;
}

function send(m: Message) { 

}

const t = getToken();

const message = {
    token: t,
}

send(message); // error

if (t) {
    send(message); // error
}

if (message.token) { 
    send(message); // still an error, which is perplexing. At this point, tsc should recognize that message meets the requirements of Message. There appears to be a confusion here.
}

send(message as Message); // valid

In general, it is advisable and safer to handle null checks through if statements rather than manual type casting. However, there can be instances where alternative options are limited.

Transforming TypeScript snapshot data in Firebase Cloud Functions into a string format for notification purposes

Update:

Answer №1

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