Exploring the canDeactivateFn syntax with Angular Documentation

Question

Exploring the canDeactivateFn syntax with Angular Documentation

As a first-year university student, I recently discovered that the canDeactivate() guard in Angular is deprecated, while the canDeactivateFn guard functions without any issues. Admittedly, navigating through official documentation is still new to me. From what I've gathered, canActivateFn and canDeactivateFn are now treated as functions rather than classes. You can directly incorporate the component you wish to utilize canDeactivateFn with in the function definition. Below is an example of how I defined my canDeactivateFn function.

/*
  My intention is to automatically save data when a user navigates away from a component.
*/
export const leaveRoute: CanDeactivateFn<EnglishComponent> = (
  // The EnglishComponent is the target component for modification
  component: EnglishComponent, 
  currentRoute: ActivatedRouteSnapshot, 
  currentState: RouterStateSnapshot, 
  nextState: RouterStateSnapshot):
  Observable<boolean | UrlTree> | Promise<boolean | UrlTree> | boolean | UrlTree  => {
    // The logic within this 'hello' block never gets executed. How can I ensure it runs when navigating away from the component?
    console.log('hello')
    component.formValue = component.form.value
    component.form.setValue(component.formValue)
    return true
  }

This is how my routing is configured.

{
        path: 'en',
        component: EnglishComponent,
        canDeactivate: [(component: EnglishComponent) => true]
},

Now, here comes my question - How do I effectively implement the canDeactivateFn guard? What additions should be made, and what aspects should be omitted? If possible, I prefer guidance from the official Angular documentation to enhance my comprehension. However, if that's not feasible, no worries at all.

I appreciate your assistance in advance :)

angular typescript

Answer 1

Answer №1

There are a couple of approaches to consider here, based on my observations. To begin with, I must disclose that I have not worked with this specific function previously.

Another point worth mentioning is that I am uncertain about the purpose of your task. It appears as though you are trying to set form data on a form that is about to be destroyed, which seems futile.

Nevertheless, assuming you have a valid reason for your approach that is not evident in the provided code, I will disregard the code and proceed with some suggestions.

Firstly, if feasible, consider avoiding direct navigation to handle this situation.

Since you are navigating away, it is likely that you are also destroying the component in some manner. In such cases, you can utilize OnDestroy:

export class MyFormComponent implements OnDestroy {
    // ...

    public ngOnDestroy(): void {
        // Perform any necessary saving operations before the component is destroyed
    }
}

I am assuming that your form component is contained within a parent element and you intend to pass the form data to the parent (via a service or an @Output emission?).

Therefore, before delving into more complex solutions involving navigation, I would recommend starting with this approach. Especially if it involves handling unsaved changes and potential pop-ups rather than intricate save operations.

However, it appears that the crux of your question revolves around integrating your method with the router. Considering your current level of familiarity, the issue might stem from anonymous functions and their usage. Here is a brief example:

Methods are essentially just like numbers and strings – they can be assigned to variables and utilized later on, similar to other data types.

const someFn = () => true;
const addStuff = (a, b) => a + b;

By calling someFn(), you will receive a value of true. The same principle applies to using addStuff as a simple addition function: const x = addStuff(1, 2);

While you could inject your code directly into the guard line, it may lead to cluttered code:

canDeactivate: [(component: EnglishComponent) => {
    console.log('hello')
    component.formValue = component.form.value
    component.form.setValue(component.formValue)
    return true
}]

Alternatively, moving your logic into a separate method and then referencing it is a cleaner approach:

const canDeactivateEnglishComponent = (component: EnglishComponent) => {
    console.log('hello')
    component.formValue = component.form.value
    component.form.setValue(component.formValue)
    return true
};

...

canDeactivate: [(component: EnglishComponent) => canDeactivateEnglishComponent(component)]

In this scenario, the canDeactivate function invokes your custom method internally. Furthermore, your method satisfies the required signature criteria, allowing you to use it directly without the need for an anonymous function wrapper:

canDeactivate: [canDeactivateEnglishComponent]

This should work; however, I recommend utilizing the ngOnDestroy lifecycle hook within your component itself to manage form data emission when it is being destroyed, instead of incorporating complex logic into the navigation guard - unless it specifically aligns with your system architecture.

Answer 2

There are a couple of approaches to consider here, based on my observations. To begin with, I must disclose that I have not worked with this specific function previously.

Another point worth mentioning is that I am uncertain about the purpose of your task. It appears as though you are trying to set form data on a form that is about to be destroyed, which seems futile.

Nevertheless, assuming you have a valid reason for your approach that is not evident in the provided code, I will disregard the code and proceed with some suggestions.

Firstly, if feasible, consider avoiding direct navigation to handle this situation.

Since you are navigating away, it is likely that you are also destroying the component in some manner. In such cases, you can utilize OnDestroy:

export class MyFormComponent implements OnDestroy {
    // ...

    public ngOnDestroy(): void {
        // Perform any necessary saving operations before the component is destroyed
    }
}

I am assuming that your form component is contained within a parent element and you intend to pass the form data to the parent (via a service or an @Output emission?).

Therefore, before delving into more complex solutions involving navigation, I would recommend starting with this approach. Especially if it involves handling unsaved changes and potential pop-ups rather than intricate save operations.

However, it appears that the crux of your question revolves around integrating your method with the router. Considering your current level of familiarity, the issue might stem from anonymous functions and their usage. Here is a brief example:

Methods are essentially just like numbers and strings – they can be assigned to variables and utilized later on, similar to other data types.

const someFn = () => true;
const addStuff = (a, b) => a + b;

By calling someFn(), you will receive a value of true. The same principle applies to using addStuff as a simple addition function: const x = addStuff(1, 2);

While you could inject your code directly into the guard line, it may lead to cluttered code:

canDeactivate: [(component: EnglishComponent) => {
    console.log('hello')
    component.formValue = component.form.value
    component.form.setValue(component.formValue)
    return true
}]

Alternatively, moving your logic into a separate method and then referencing it is a cleaner approach:

const canDeactivateEnglishComponent = (component: EnglishComponent) => {
    console.log('hello')
    component.formValue = component.form.value
    component.form.setValue(component.formValue)
    return true
};

...

canDeactivate: [(component: EnglishComponent) => canDeactivateEnglishComponent(component)]

In this scenario, the canDeactivate function invokes your custom method internally. Furthermore, your method satisfies the required signature criteria, allowing you to use it directly without the need for an anonymous function wrapper:

canDeactivate: [canDeactivateEnglishComponent]

This should work; however, I recommend utilizing the ngOnDestroy lifecycle hook within your component itself to manage form data emission when it is being destroyed, instead of incorporating complex logic into the navigation guard - unless it specifically aligns with your system architecture.

Exploring the canDeactivateFn syntax with Angular Documentation

Answer №1

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