Restrict Angular 2 Component to specific ancestor Component

Question

Restrict Angular 2 Component to specific ancestor Component

Is it possible in Angular 2 to restrict a Component so that it can only appear within a specific parent element on a page? In other words, the Component should only be allowed if it has a certain parent element. Here is an example:

Allowed:

<parent>
  <child></child>
</parent>

Not Allowed: (does not have <parent> as a parent element)

<child></child>

I want the parent Component to be transcluded and the <child> tag to be optional, so I cannot simply do:

@Component({
  /*...*/
  selector: 'parent',
  template: `<child></child>`
});

Any suggestions on how to achieve this?

javascript angular typescript

Answer 1

Answer №1

That method should get the job done.

Main section :

@Component({
  selector: 'main',
  template: '<ng-content></ng-content>'
})

export class MainSection {

}

Subsection :

@Component({
  selector: 'subsection',
  template: ''
})
export class Subsection {
  constructor(parent: MainSection){
    // will result in a no provider error if parent is not defined
  }
}

Afterwards, you can utilize your sections as needed:

<main><subsection></subsection></main> <!-- functions correctly -->
<subsection></subsection> <!-- does not work -->

Remember that by injecting the main section into the subsection, the subsection can actually be nested further without causing an error.

Answer 2

That method should get the job done.

Main section :

@Component({
  selector: 'main',
  template: '<ng-content></ng-content>'
})

export class MainSection {

}

Subsection :

@Component({
  selector: 'subsection',
  template: ''
})
export class Subsection {
  constructor(parent: MainSection){
    // will result in a no provider error if parent is not defined
  }
}

Afterwards, you can utilize your sections as needed:

<main><subsection></subsection></main> <!-- functions correctly -->
<subsection></subsection> <!-- does not work -->

Remember that by injecting the main section into the subsection, the subsection can actually be nested further without causing an error.

Answer 3

Answer №2

An enhanced version of the provided solution allows for a more user-friendly error message by utilizing the Optional decorator and verifying for null:

@Component({
  selector: 'child'
})
export class ChildComponent {
  constructor(@Optional() parent: ParentComponent){
    if (parent === null) 
      throw new Error("ChildComponent can only be utilized within ParentComponent context")
  }
}

Answer 4

An enhanced version of the provided solution allows for a more user-friendly error message by utilizing the Optional decorator and verifying for null:

@Component({
  selector: 'child'
})
export class ChildComponent {
  constructor(@Optional() parent: ParentComponent){
    if (parent === null) 
      throw new Error("ChildComponent can only be utilized within ParentComponent context")
  }
}

Restrict Angular 2 Component to specific ancestor Component

Answer №1

Main section :

Subsection :

Answer №2

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