Sign up for an observable only when a specific variable has been modified

Question

Sign up for an observable only when a specific variable has been modified

I am facing an issue where I need to restrict the usage of rxjs's subscribe method to only certain property changes. I attempted to achieve this using distinctUntilChanged, but it seems like there is something missing in my implementation.

The specific requirement is for the subscribe function to be triggered only when the data.members[] property undergoes a change.

this.myService.loadData(this.data.id)
  .distinctUntilChanged()
  .subscribe(data => {
    this.data = data;
    console.log("data changed", data);
});

I would appreciate guidance on how to effectively respond to distinct changes in this scenario.

javascript angularjs rxjs

Answer 1

Answer №1

After reviewing the Rxjs v4 documentation, it appears that you can accomplish your goal using

Rx.Observable.prototype.distinctUntilChanged([keySelector], [comparer])

. This allows you to select a specific property to monitor for changes and use a comparer parameter to check for equality.

In Rxjs v5, there are both distinctUntilKeyChanged and distinctUntilChanged operators with similar functionalities.

If you need further guidance on implementation, you can refer to example usage in the tests: [distinctUntilChanged-spec.ts, distinctUntilKeyChanged-spec.ts]

If you encounter any difficulties while setting this up, feel free to share what you've attempted so far.

Answer 2

After reviewing the Rxjs v4 documentation, it appears that you can accomplish your goal using

Rx.Observable.prototype.distinctUntilChanged([keySelector], [comparer])

. This allows you to select a specific property to monitor for changes and use a comparer parameter to check for equality.

In Rxjs v5, there are both distinctUntilKeyChanged and distinctUntilChanged operators with similar functionalities.

If you need further guidance on implementation, you can refer to example usage in the tests: [distinctUntilChanged-spec.ts, distinctUntilKeyChanged-spec.ts]

If you encounter any difficulties while setting this up, feel free to share what you've attempted so far.

Answer 3

Answer №2

.distinctUntilChanged((data) => { return data.members; })
is effective! How can I detect changes in multiple arrays like members, relations, and children?

I am interested in responding to array modifications (additions/deletions).

To perform a deep comparison, utilize angular.equals.

this.myService.loadData(this.data.id)
  .distinctUntilChanged((data) => (data.members), (a,b) => (angular.equals(a,b))
  .subscribe(data => {
    this.data = data;
    console.log("data changed", data);
});

For further insights on distinctUntilChanged, refer to the RxJS distinctUntilChanged API Reference.

If you wish to learn more about angular.equals, check out the AngularJS angular.equals API Reference.

Answer 4

.distinctUntilChanged((data) => { return data.members; })
is effective! How can I detect changes in multiple arrays like members, relations, and children?

I am interested in responding to array modifications (additions/deletions).

To perform a deep comparison, utilize angular.equals.

this.myService.loadData(this.data.id)
  .distinctUntilChanged((data) => (data.members), (a,b) => (angular.equals(a,b))
  .subscribe(data => {
    this.data = data;
    console.log("data changed", data);
});

For further insights on distinctUntilChanged, refer to the RxJS distinctUntilChanged API Reference.

If you wish to learn more about angular.equals, check out the AngularJS angular.equals API Reference.

Sign up for an observable only when a specific variable has been modified

Answer №1

Answer №2

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