Undo functionality allows users to revert changes made in an application to a previous state. In Angular applications, one way to implement undo functionality is by using Immer, a library that simplifies state management and immutability.

Immer makes it easy to work with immutable data structures by allowing you to write code as if you were directly mutating the state. Under the hood, Immer uses a concept called “structural sharing” to efficiently create new immutable state trees.

To implement undo functionality with Immer in an Angular application, follow these steps:

Step 1: Install Immer

First, install Immer by running the following command in your Angular project directory:

npm install immer

Step 2: Set up app state

In your Angular application, define the state of your app using an Immer draft. A draft is a mutable version of an object that can be used to apply changes and generate a new state.

import produce, {Draft} from 'immer';

interface AppState {
  // Define your app state properties here
}

const initialState: AppState = {
  // Initialize your app state properties here
};

export const appReducer = produce((draft: Draft<AppState>, action) => {
  // Implement your state mutations here
}, initialState);

Step 3: Create an undo stack

Next, create an undo stack to store the previous states of your app. This stack will be used to revert changes when the user triggers the undo action.

import {Stack} from 'immutable';

const undoStack: Stack<AppState> = Stack<AppState>().push(initialState);

// Function to push a new state into the undo stack
const pushStateToUndoStack = (state: AppState) => {
  undoStack.push(state);
};

// Function to retrieve the last state from the undo stack
const getLastStateFromUndoStack = (): AppState => {
  return undoStack.peek();
};

// Function to revert to the previous state from the undo stack
const undoLastState = (): AppState | undefined => {
  if (undoStack.size > 1) {
    undoStack.pop();
    return getLastStateFromUndoStack();
  }
  return undefined;
};

Step 4: Dispatch undo actions

In your Angular components, dispatch undo actions whenever the user triggers the undo functionality.

import {Component} from '@angular/core';
import {Store} from '@ngrx/store';

export class MyComponent {
  constructor(private store: Store) {}

  undo() {
    const lastState = getLastStateFromUndoStack();
    if (lastState) {
      this.store.dispatch({type: 'UNDO', payload: lastState});
    }
  }
}

Step 5: Update the state using Immer

In your app reducer, handle the ‘UNDO’ action by updating the state using Immer’s produce function. This will generate a new immutable state with the last state from the undo stack.

export const appReducer = produce((draft: Draft<AppState>, action) => {
  switch (action.type) {
    case 'UNDO':
      return action.payload; // Replace the current state with the last state from the undo stack
    default:
      // Implement other state mutations
  }
}, initialState);

That’s it! You have successfully implemented undo functionality using Immer in your Angular application. Users can now revert changes to a previous state by triggering the undo action.

#hashtags #Immer #Angular