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https://github.com/BeardScript/history-actions

Action manager framework with undo/redo
https://github.com/BeardScript/history-actions

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Action manager framework with undo/redo

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# history-actions

Action manager framework with undo/redo.



This lightweight package provides a simple and flexible pattern to define user actions that can be done and undone through the **historyManager**, while letting you keep track of instances within your state, no matter how complex they could be. You can record multiple actions within a single **ChangeLog** and undo them all in one call.



- Simple.

- Lightweight.

- Flexible.



# Instructions



## Install



```bash



npm install history-actions --save



```



## Define an Action



An **Action** defines the way a mutation is done and undone. For a better result, you should granulate your actions as much as possible. An **Action** should do one thing only.



An **Action** should not mutate the state of an object, but trigger the mutation within it. In OOP an object should mutate its own state, so even when you set a property from an **Action**, you should be triggering the setter on that property's definition. So it's fair to say that an **Action** is by all means a controller.



Here's an example of an **Action**:



```typescript



import { Action } from 'history-actions';

import { myTestState } from './MyTestState';



export class SetHeight extends Action {

  private _value: number;

  private _undoValue: number;



  constructor( value: number ) {

    super();

    this._value = value;

    this._undoValue = myTestState.height;

  }



  do() {

    myTestState.height = this._value;

  }

  

  undo() {

    myTestState.height = this._undoValue;

  }

  

  // OPTIONAL: by default is defined in the superclass as follows

  redo() {

    this.do();

  }

}



```



Let's look at the above code more in-depth:



### The class



Create a class with the name of the action you are defining and make sure it extends Action.



```typescript



import { Action } from 'history-actions';



export class MyAction extends Action {

...

}



```



If you are using typescript, which is highly recommended, it will force the implementation of the abstract **do()** and **undo()** methods.



### Properties and constructor



These will vary depending on the **Action**. You are free to provide whatever properties your class will need in order to **do()**, **undo()** and if necessary, to **redo()** an **Action**.



### The *action.do()* method



Here is where you should define how to mutate whatever it is you are mutating.



### The *action.undo()* method



Here is where you define how to reverse whatever was done in the **do()** method.



CAUTION: you should never call this method. Use **historyManager.undo()** instead.



### The *action.redo()* method



Normally you won't need to define this method, since by default it's defined to call **do()** but in case you need additional boilerplate to redo whatever was undone, you should define it.



CAUTION: you should never call this method. Use **historyManager.redo()** instead.



## historyManager



The **historyManager** gives you a simple interface to **record()** multiple actions within a **ChangeLog** that you can **save()** in order to **undo()** it and **redo()** it.



### Example



Now to the fun part.



Once your Actions are defined you should use them, right? Otherwise they'll be sitting there bored, and feeling useless.

Let's see them in action.



```typescript



import { historyManager } from 'history-actions';

import { MyAction } from './Actions/MyAction';



// Instantiate an 

const action = new MyAction();



// Record it

historyManager.record(action);



// Run it

action.do(); 

// or action.asyncDo()



// Save the  you are recording. 

historyManager.save();



```



After calling **save()**, the next recorded action will be pushed into a new **ChangeLog**.



Alternatively to calling **action.do()** you can call **action.asyncDo()** which is simply an asynchronous wrapper that calls **do()**.



You can record multiple actions in a single **ChangeLog**. That is where this pattern shines. You can record a series of actions and undo them all in one call.



```typescript



import { historyManager } from 'history-actions';

import { MyAction } from './Actions/MyAction';



// Instantiate one or more actions

const action1 = new MyAction();

const action2 = new MyAction();



// Record them

historyManager.record(action1);

historyManager.record(action2);



// Run them

action1.do();

action2.do();



// Save the  you are recording. 

historyManager.save();



```



### undo() | redo() | clear()



```typescript



import { historyManager } from 'history-actions';



// Undo the last saved 

historyManager.undo()



// Redo the last undone 

historyManager.redo()



// Clear all change logs and reset

historyManager.clear()



```



### Utilities



```typescript



import { historyManager } from 'history-actions';



// Returns the last recorded  in the current  being recorded.

historyManager.getLastRecordedAction();



// Returns the current  being recorded.

historyManager.getRecording();



// Set/Get the max number of undo's allowed (default: 20).

historyManager.maxLogs = 20;



// Returns true if an Action has been pushed to the current .

const isRecording: boolean = historyManager.isRecording();



```



### What is a *ChangeLog*?



A *ChangeLog* consists on one or more actions that trigger mutations within the state of your app. It's a perceived change for the user which they might want to undo.



The **historyManager** records change logs. 



When you **historyManager.record( action )** you are basically adding the action to the current **ChangeLog** being recorded.



When you **historyManager.save()** you are closing the **ChangeLog** being recorded, so that a new one can be created.



**Why not just undoing/redoing a single action?** 



Well, let's say you want to **Add( objectInstance )**. Then, you simply create an Action **AddObjectInstance** and call the **Add( objectInstance )** method inside. Let's also asume that you do the same for **Remove()**, and now you want to perform a **Switch()**. So... you could define a **SwitchObjectInstance** Action, or you could reutilize the **Add** and **Remove** you already have, and record them in a single change log. This is just a very simple example of how this pattern scales.