What could be causing the issue with converting a Firestore timestamp to a Date object in my Angular app?

Currently, I am developing an Angular project that involves using a FireStore database. However, I have encountered a problem with the setup.

Within my Firestore database, I have documents structured like the example shown in this image: https://i.sstatic.net/7z8M6.png

The fields start and end are defined as TimeStamp fields in Firestore, as depicted in the provided screenshot.

In my service class, I fetch all these documents from the collection and return them as a list of Observable using the following method:

getEvents(): Observable<any[]> {
    this.items = this.db.collection('calendar').valueChanges();

    return this.items;
 }

Upon calling the ngOnInit() method in my component class, I perform the following actions:

ngOnInit() {

    this.eventService.getEvents().subscribe(events => { this.events = events.map((event) => {

    console.log("START: ", event.start);

    var date = new Date(0);
    date.setUTCSeconds(event.start);

    var hour = date.getHours();

    console.log("START DATE: ", date);
    console.log("START HOUR: ", hour);
    // ...
}

Here lies the issue: the value retrieved for event.start is not a standard date format but instead an object represented as follows:

START:  t {seconds: 1487257200, nanoseconds: 0}

This object seems to represent the date, but I am unsure how to convert it back into a valid Date object.

I attempted the conversion in the following manner:

var date = new Date(0);
date.setUTCSeconds(event.start);

However, this approach yields an incorrect date:

START DATE:  Sun Feb 16 3986 07:00:00 GMT-0800 (Pacific Standard Time)

While the month and day (Feb 16) are accurate, the year is completely off (3986 instead of 2017).

What am I missing? What is the correct method to obtain a valid Date object from the retrieved Firestore Timestamp?

Answer №1

Firestore timestamps have a unique structure that differs from traditional JS Date().

To convert a timestamp to a JS date, you must utilize the specific method provided by Firestore for timestamps.

In your code:

event.start should be event.start.toDate()

It's important for your IDE to recognize the object type in order to suggest available methods. When using AngularFire, specifying the type will ensure proper method suggestions. If the type is too generic (like "any"), the IDE may not provide accurate methods and could potentially throw errors like "method doesn't exist on type any".

Answer №2

If you want to convert Timestamps and map observable arrays to Dates in Angular, you can utilize the Timestamps toDate() function. Here's how you can achieve this:

// To make it cleaner, create a custom type. It's recommended to do this in a separate file. 
// You can learn more about type aliases here: https://www.typescriptlang.org/docs/handbook/advanced-types.html#type-aliases

type ReturnType = {start: Date, end: Date, title: string};

// Modify the function to return the newly created type

getEvents(): Observable<ReturnType[]> {
    this.items = this.db.collection('calendar').valueChanges()
        .pipe(map(tArr => // Use pipe to transform an observable or subject without subscribing. Refer to: https://rxjs-dev.firebaseapp.com/guide/operators
            tArr.map(t => { // Map the array of objects containing Timestamps to dates
                t.start = t.start.toDate();
                t.end = t.end.toDate();
                return t;
            })
        )) as Observable<ReturnType[]>;

    return this.items;
}

Answer №3

Your approach to creating a JS Date object is incorrect. The proper way to instantiate a date is by providing milliseconds as input.

var date = new Date(event.start.seconds * 1000);

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