Ways to modify Angular pipe without specifying data types

I am in the process of extracting an Angular pipe from an application to a library. The current pipe is tied to specific types, but I want to change it to use generic types while maintaining type safety.

Original Pipe:

  import { Pipe, PipeTransform } from ...
  import { MyCustomTypeOne } from ...
  import { MyCustomTypeTwo } from ...
  import { MyCustomService } from ...

  @Pipe({ name: 'customPipe' })
export class CustomPipe implements PipeTransform {

  constructor(private myService: MyCustomService) {}

  transform(value: MyCustomTypeOne, details: MyCustomTypeTwo): string {
    return this.MyCustomService.getResult(
      value.customPropertyOne,
      value.customPropertyTwo,
      details.customPropertyOne
    );
  }
}

How can I modify this code so that I don't have to rely on specific custom types when moving it to a library?

Revised Approach:

I have a requirement to keep the types out of the library. Would defining interfaces with specific/generic properties at the beginning of the file be considered bad practice - does this approach maintain type safety?

Example:

  ...

  interface MyCustomTypeOne {
    customPropertyOne: any;
    customPropertyTwo: any;
    [key: string]: any;
  }

  interface MyCustomTypeTwo {
    customPropertyOne: any;
    [key: string]: any;
  }

  @Pipe({ name: 'customPipe' })
  export class CustomPipe implements PipeTransform {

  constructor(private myService: MyCustomService) {}

  transform(value: MyCustomTypeOne, details: MyCustomTypeTwo): string {
  ...

Answer №1

The issue here lies in the fact that you are targeting specific properties within certain types. For instance, you have MyCustomTypeOne and MyCustomTypeTwo, specifically looking for .customPropertyOne and .customPropertyTwo.

As a result, this pipe function will only function with types that contain these properties. If you were to extract them outside of the library, it would involve relocating your models (MyCustomType*) into the library itself rather than leaving them external.

In essence, the main adjustment needed in your pipe function would be related to where modules are being imported from.

Furthermore, you mentioned the use of generics. It seems unnecessary in this case as generics typically relate to return types. While there may be scenarios where generics can be used without affecting output directly, implementing them might look something like this:

  transform<T, U>(value: T, details: U): string {
    return 'something';
  }

or

  transform<T>(value: T, details: T): string {
    return 'something';
  }

However, bear in mind that when employing generics like this, both T and U are generic types, meaning someone could input a Date object which could potentially lead to issues since Date does not possess properties like customPropertyOne. It's also important to note that the transform function is invoked by Angular, not explicitly called by you, so passing in generic types may not actually occur.

To simplify, it might be more beneficial to relocate your models into the library instead of attempting to make them "generic".

Answer №2

Incorporating types within the library can enhance its functionality within this specific scope.

Consider organizing types inside the pipe, or in close proximity to it for more streamlined access within the library.

While using any is a possibility, I strongly advise against it as it may compromise specificity and accuracy.

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