When initializing a variable in Typescript, it is important to consider that the object may potentially be undefined

Question

When initializing a variable in Typescript, it is important to consider that the object may potentially be undefined

I've encountered a problem with a component in my app:

@Component({
  selector: 'app-payment-intent',
  templateUrl: './payment-intent.component.html',
  styleUrls: ['./payment-intent.component.css']
})
export class PaymentIntentComponent implements OnInit {

  static = false;
  @ViewChild(StripeCardComponent, this.static) card: StripeCardComponent;

However, during app compilation, I receive the following error:

Object is possibly 'undefined'

The issue seems to stem from the static = false variable, which causes

@ViewChild(StripeCardComponent, this.static) card

to potentially be interpreted as undefined. Despite the variable being initialized as false, this error persists.

Any advice on resolving this issue would be greatly appreciated!

Thank you!

angular typescript undefined

Answer 1

Answer №1

The @ViewChild element serves as a decorator in this particular scenario. To fully grasp the issue at hand, it is essential to have a deep understanding of how decorators function and their application to methods.

Here is the original code snippet:

function decorator(value?:any) {
  return function <T>(target: unknown, propertyKey: string, descriptor: TypedPropertyDescriptor<T>): void {
    console.log('value:', value);
  };
}

class Bar {
    @decorator(this)
    public foo():void {}
}

Upon compilation, the code transforms into:

// __decorate and __metadata declarations skipped

function decorator(value) {
  return function (target, propertyKey, descriptor) {
    console.log('value:', value);
  };
}

class Bar {
  foo() { }
}

__decorate([
  decorator(this),
  __metadata("design:type", Function),
  __metadata("design:paramtypes", []),
  __metadata("design:returntype", void 0)
], Bar.prototype, "foo", null);

Following the compilation process, it becomes evident that decorators alter the prototype class, not its instance. Consequently, when you pass 'this' in the argument 'this.static' to the decorator, it does not reference any context, leading to an undefined value.

Answer 2

The @ViewChild element serves as a decorator in this particular scenario. To fully grasp the issue at hand, it is essential to have a deep understanding of how decorators function and their application to methods.

Here is the original code snippet:

function decorator(value?:any) {
  return function <T>(target: unknown, propertyKey: string, descriptor: TypedPropertyDescriptor<T>): void {
    console.log('value:', value);
  };
}

class Bar {
    @decorator(this)
    public foo():void {}
}

Upon compilation, the code transforms into:

// __decorate and __metadata declarations skipped

function decorator(value) {
  return function (target, propertyKey, descriptor) {
    console.log('value:', value);
  };
}

class Bar {
  foo() { }
}

__decorate([
  decorator(this),
  __metadata("design:type", Function),
  __metadata("design:paramtypes", []),
  __metadata("design:returntype", void 0)
], Bar.prototype, "foo", null);

Following the compilation process, it becomes evident that decorators alter the prototype class, not its instance. Consequently, when you pass 'this' in the argument 'this.static' to the decorator, it does not reference any context, leading to an undefined value.

Answer 3

Answer №2

If you check out the Angular documentation on Migration to Static Queries, you'll see that the second parameter for @ViewChild should be of type { static: boolean }. Therefore, you need to adjust your code as follows:

@ViewChild(StripeCardComponent, { static: this.static }) card: StripeCardComponent;

Alternatively, it's recommended to directly set it to false, as this condition takes effect during initialization:

@ViewChild(StripeCardComponent, { static: false }) card: StripeCardComponent;

Answer 4

If you check out the Angular documentation on Migration to Static Queries, you'll see that the second parameter for @ViewChild should be of type { static: boolean }. Therefore, you need to adjust your code as follows:

@ViewChild(StripeCardComponent, { static: this.static }) card: StripeCardComponent;

Alternatively, it's recommended to directly set it to false, as this condition takes effect during initialization:

@ViewChild(StripeCardComponent, { static: false }) card: StripeCardComponent;

When initializing a variable in Typescript, it is important to consider that the object may potentially be undefined

Answer №1

Answer №2

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