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In NGXS we have getState() to get the current state. Is there a way to get the previous state from the store? I am looking for a solution to this as I have to implement Undo/Redo kind of functionality. Thanks!

Mathi
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4 Answers4

3

You can use the store.snapshot() method to get the snapshot of the store at that particular time. You can store the snapshot in a variable and then, in case of a re-roll, just use store.reset() with the snapshot.

export class MyComponent {

  private initialSnapshot: MyStoreStateModel;

  constructor(private store: Store){
    this.initialSnapshot = store.snapshot();
  }

  // ... component logic / state modification logic

  rollback = () => this.store.reset(this.initialSnapshot); 
}

Adjust to your needs...

Hope this helps a little :-)

Heehaaw
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@Mark Whitfield is correct that there is no direct way to get the previous state with NGXS. Using NGXS I had a use case where I wanted to know the previous value to perform an undo-style operation.

I used the regular NGXS @Selector syntax to tap into the state slice I was interested in, then in I subscribed directly to that Observable and used the rxjs pairwise operator to give me the new emitted value and the previous value. Worked well for the way I wanted to consume those values so it might fit what you are after.

Garth Mason
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There is no way to get the previous state by default, but you can definitely create a service that monitors the state and pushes a copy into its own stack. You can then restore this state using the reset method on the store.

You would probably use the select and reset methods of the store. See here for more info: https://ngxs.gitbook.io/ngxs/concepts/store#selecting-state

Mark Whitfeld
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-1

You can use "redux-undo" from npm to implement undo and redo. It is pretty simple and straight forward. You can find the docs here

Chandra Sagar
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