Typescript: How to reassign static function in child class?-CodePudding

I have a parent class like so:

class SomeClass {

  public someProperty: number | undefined;

  constructor(value: number) {
    this.someProperty = value;
  }

  public on(eventType: string, fn: Function) {

  }
}

class Parent {

  protected static getTransform(value: number) {
    return value   180;
  }

  public transform: SomeClass;

  constructor(value: number) {
    this.transform = this.createTransform(value);
  }

  protected createTransform(value: number) {
    const transform = new SomeClass(value);
    transform.on('rotate', this.rotate);
    return transform;
  }

  protected rotate(event: any) {
    this.transform.someProperty = Parent.getTransform(event.transform);
  }
}

And I need to implement child class that has different logic of transform property calculation. I need something, like so:

class Child extends Parent {

  protected static getTransform(value: number) {
    return value   90;
  }

  constructor(value: number) {
    super(value);
  }
}

I haven't faced any errors or something else, but my approach doesn't work, nothing changed. How to implement same? Playground

CodePudding user response：

... protected (which allows access from the same class and its subclasses, but not objects of a different class) ... Wiki: OOP

To clear the Member Visibility concept, here is a demo of your code (Please see the comments):

class SomeClass {

  public someProperty: number | undefined;

  constructor(value: number) {
    this.someProperty = value;
  }

  public on(eventType: string, fn: Function) {

  }
}

class Parent {

  protected static getTransform(value: number) {
    return value   180;
  }

  public transform: SomeClass;

  constructor(value: number) {
    this.transform = this.createTransform(value);
  }

  protected createTransform(value: number) {
    const transform = new SomeClass(value);
    transform.on('rotate', this.rotate);
    return transform;
  }

  protected rotate(event: any) {
    this.transform.someProperty = Parent.getTransform(event.transform);
  }
}

class Child extends Parent {

  protected static getTransform(value: number) {
    return value   90;
  }

  constructor(value: number) {
    super(value);
  }
}

class Example extends Child {
  constructor(value: number) {
      super(value)
    console.log(`In Example:`, Child.getTransform(700)) // this line will be called when `new Example()`
  }

  public static getTransform(value: number) {
    return Child.getTransform(600); // call parent method which is protected is valid
  }

}

// Example use cases:

console.log(`Call Child:`, Child.getTransform(800)) //  this will throw error:
// Property 'getTransform' is protected and only accessible within class 'Child' and its subclasses.

new Example(700) // inheritance can call parent method which is protected

console.log(`Call Example:`, Example.getTransform(1000)) // a function call that call parent protected method is ok.

TypeScript Playground <- You can click the Run button the see the result and the Errors tab to see the error messages.

CodePudding user response：

I am not sure why you want to reassign a static function.. in your case you should override the rotate() function in Child and use the Child static method instead:

  protected rotate(event: any) {
    this.transform.someProperty = Child.getTransform(event.transform);
  }