ExitDecorator in TypeScript

Question

ExitDecorator in TypeScript

Introduction:

In my current setup, I have an object called `Item` that consists of an array of `Group(s)`, with each group containing an array of `User(s)`. The `Item` object exposes various APIs such as `addUser`, `removeUser`, `addGroup`, `removeGroup`, `addUnit`, and `removeUnit`. Every time one of these actions is taken, the `rank` property of each user within a certain group needs to be recalculated.

I am seeking a solution where the method `calcRank` is automatically triggered at the end of each API action without the need for explicit invocation. Something akin to an `OnExit` decorator would be ideal.

typescript

Answer 1

Answer №1

The Advice Design Pattern shows how to easily implement dynamic behavior in JavaScript:

function beforeAction(modifyBehavior) {
  return function(method) {
    return function beforeHandler(...args) {
      modifyBehavior.apply(this, args);
      return method.apply(this, args);
    };
  };
}

function afterAction(modifyBehavior) {
  return function(method) {
    return function afterHandler(...args) {
      const result = method.apply(this, args);
      modifyBehavior.apply(this, [args, result]);
      return result;
    };
  };
}

const defaultFunc = _ => _;

function applyAdvice({before: beforeModifier = defaultFunc, after: afterModifier = defaultFunc, skip: []}) {
  return function(Class) {
    Object.keys(Class.prototype).forEach(function(methodName) {
      if (!skip.contains(methodName)) {
        const method = Class.prototype[methodName];
        const afterDecorator = afterAction(afterModifier);
        const beforeDecorator = beforeAction(beforeModifier);
        Class.prototype[methodName] = afterDecorator(beforeDecorator(method));
      }
    });
  };
}


@applyAdvice({
  after() {
    this.updateRank();
  },
  skip: ['updateRank']
})
class Item {
  addUser() {}
  removeUser() {}
  addGroup() {}
  removeGroup() {}
  addUnit() {}
  removeUnit() {}
  updateRank() {}
}

Answer 2

The Advice Design Pattern shows how to easily implement dynamic behavior in JavaScript:

function beforeAction(modifyBehavior) {
  return function(method) {
    return function beforeHandler(...args) {
      modifyBehavior.apply(this, args);
      return method.apply(this, args);
    };
  };
}

function afterAction(modifyBehavior) {
  return function(method) {
    return function afterHandler(...args) {
      const result = method.apply(this, args);
      modifyBehavior.apply(this, [args, result]);
      return result;
    };
  };
}

const defaultFunc = _ => _;

function applyAdvice({before: beforeModifier = defaultFunc, after: afterModifier = defaultFunc, skip: []}) {
  return function(Class) {
    Object.keys(Class.prototype).forEach(function(methodName) {
      if (!skip.contains(methodName)) {
        const method = Class.prototype[methodName];
        const afterDecorator = afterAction(afterModifier);
        const beforeDecorator = beforeAction(beforeModifier);
        Class.prototype[methodName] = afterDecorator(beforeDecorator(method));
      }
    });
  };
}


@applyAdvice({
  after() {
    this.updateRank();
  },
  skip: ['updateRank']
})
class Item {
  addUser() {}
  removeUser() {}
  addGroup() {}
  removeGroup() {}
  addUnit() {}
  removeUnit() {}
  updateRank() {}
}

ExitDecorator in TypeScript

Answer №1

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