Accessing a TypeScript variable in Angular2 and binding it to the HTML DOM

Question

Accessing a TypeScript variable in Angular2 and binding it to the HTML DOM

While I have experience with AngularJS, delving into Angular2 has proven to be a new challenge for me. Understanding the ropes is still a work in progress.

In my list of files, there's a home.ts and a home.html

Within my home.ts, this snippet resides:

@Component({
  selector: 'page-home',
  templateUrl: 'home.html'
})
export class HomePage {

  userData:any;

  constructor(
    public navCtrl: NavController,
    private storage: Storage,
    private database: AngularFireDatabase) {
      this.storage.get('user').then((result) => {
        this.userData = result;
      });

  }

A user-related data point is stored in localStorage which I'm assigning to userData..

However, in my .html file, an attempt to display information from the userData variable within a span element hasn't been smooth sailing:

<span id="userName">{{userData.firstName}}</span>

Every time, I run into a flood of errors citing

Cannot read property 'firstName' of undefined

...

I'll appreciate any insights on bridging the gap between the userData variable and its appearance in my html code. Many thanks!

javascript angular typescript

Answer 1

Answer №1

Ensure that this.storage.get('user') has been resolved before moving forward with your then statement. If userData is undefined at the time, attempting to access userData.firstName will result in an error message stating 'Cannot read property 'firstName' of undefined'.

To resolve this issue, consider implementing the following:

<span *ngIf="userData" id="userName">{{userData.firstName}}</span>

This approach allows you to display the value on the screen only after the promise has been successfully resolved.

Answer 2

Ensure that this.storage.get('user') has been resolved before moving forward with your then statement. If userData is undefined at the time, attempting to access userData.firstName will result in an error message stating 'Cannot read property 'firstName' of undefined'.

To resolve this issue, consider implementing the following:

<span *ngIf="userData" id="userName">{{userData.firstName}}</span>

This approach allows you to display the value on the screen only after the promise has been successfully resolved.

Answer 3

Answer №2

In situations like this, my go-to solution is to utilize the elvis operator in my binding. For your specific case, it would look something like this:

<span id="userName">{{userData?.firstName}}</span>

The issue arises because Angular attempts to display the value while your asynchronous request is still being resolved. As a result, it tries to access the first name property on an undefined object, leading to the exception you're encountering.

Another approach (although not my preferred method) is to assign an initial value to userData. Here's an example:

userData: any = {};

Answer 4

In situations like this, my go-to solution is to utilize the elvis operator in my binding. For your specific case, it would look something like this:

<span id="userName">{{userData?.firstName}}</span>

The issue arises because Angular attempts to display the value while your asynchronous request is still being resolved. As a result, it tries to access the first name property on an undefined object, leading to the exception you're encountering.

Another approach (although not my preferred method) is to assign an initial value to userData. Here's an example:

userData: any = {};

Accessing a TypeScript variable in Angular2 and binding it to the HTML DOM

Answer №1

Answer №2

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