One common requirement in modern web applications is to provide an undo functionality, allowing users to revert back to previous states of an application. In this blog post, we will explore how to implement undo functionality using Immer, a popular immutable state management library, in Angular applications.

What is Immer?

Immer is a JavaScript library that allows for easy and efficient immutable state management. It provides a simple API to produce the next immutable state by directly mutating a draft state. Under the hood, Immer uses the concept of structural sharing to efficiently update the state while keeping memory usage low.

Setting up the project

Before we start implementing the undo functionality, let’s set up a basic Angular project:

ng new undo-app
cd undo-app
ng generate component undo-app

This will generate a new Angular project with a single component named ‘undo-app’.

Implementing undo functionality

To implement undo functionality, we need to maintain a stack of previous states and provide actions to undo and redo the state changes.

First, let’s install Immer by running the following command:

npm install immer

Once Immer is installed, we need to import it in our component:

import { produce, applyPatches, enablePatches, enableMapSet } from 'immer';

We enable patches and Map/Set by invoking the respective enable functions. This is necessary to support undo/redo operations on complex data structures:

enablePatches();
enableMapSet();

Next, we define our state and initialize it with an empty array of states and a pointer to the current state:

state = {
  states: [],
  pointer: -1
};

Now, let’s create a function to handle state updates using Immer:

updateState(updater: (draft: Draft<State>) => void) {
  this.state.states = produce(this.state.states, updater);
  this.state.pointer = this.state.states.length - 1;
}

The updateState function takes an updater function, which will be used to apply the state changes using Immer’s produce function. After updating the state, we also update the pointer to the current state.

To implement undo and redo functionalities, we need two additional functions:

undo() {
  if (this.state.pointer > 0) {
    this.state.pointer--;
  }
}

redo() {
  if (this.state.pointer < this.state.states.length - 1) {
    this.state.pointer++;
  }
}

Finally, we can use these functions in our component’s template to handle undo/redo actions:

<button (click)="undo()">Undo</button>
<button (click)="redo()">Redo</button>

Conclusion

In this blog post, we have seen how to implement undo functionality using Immer in Angular applications. By using Immer’s powerful API for immutable state management, we can easily maintain a history of previous states and provide undo/redo functionality to our users.

Implementing undo functionality not only enhances the user experience but also provides users with a safety net to revert back to previous states, reducing the chances of data loss.

Now that you are familiar with how to implement undo functionality with Immer in Angular applications, you can start incorporating it into your own projects. Happy coding!

#Angular #Immer #UndoFunctionality