Minimize the occurrence of errors by focusing on parameter piping transformations in Angular

Question

Minimize the occurrence of errors by focusing on parameter piping transformations in Angular

Recently, I created a custom transform pipe in order to condense a collection of objects. The implementation of the SumPipe looks like this:

export class SumPipe implements PipeTransform {
  transform(items: ListCount[], attr: string): number {
    return items.reduce((a, b) => a + b[attr], 0);
  }
}

Here is the model for ListCount used in this transform:

export interface ListCount {
  centre?: string;
  cause?: string;
  Time?: number;
}

However, upon testing, I encountered an error message stating:

 error TS7053: Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'ListCount'

If anyone has any insights or solutions to this issue, I would greatly appreciate the assistance.

angular typescript pipe reduce

Answer 1

Answer №1

The reason for this error is that the variable attr is a string, which is not a recognized property of the object ListCount.

To resolve this issue, you can implement the following solution:

export class SumPipe implements PipeTransform {
  transform(items: ListCount[], attr: keyof ListCount): number {
    return items.reduce((a, b) => a + b[attr], 0);
  }
}

Answer 2

The reason for this error is that the variable attr is a string, which is not a recognized property of the object ListCount.

To resolve this issue, you can implement the following solution:

export class SumPipe implements PipeTransform {
  transform(items: ListCount[], attr: keyof ListCount): number {
    return items.reduce((a, b) => a + b[attr], 0);
  }
}

Answer 3

Answer №2

As detailed in the HTN response, by utilizing attr: keyof ListCount, you can refine the typings for the attr parameter. However, since ListCount contains properties with both string and number values, it is essential to verify if the attribute retrieved from b is of type number using typeof.

export class SumPipe implements PipeTransform {
  transform(items: ListCount[], attr: keyof ListCount): number {
    return items.reduce((a, b) => {
      // obtain the value of `attr` from `b`
      const value = b[attr];
      // check if the type of `b[attr]` is a number
      // - perform addition if true
      // - else, return the existing `a` value
      return typeof value === 'number' ? a += value : a;
    }, 0);
  }
}

Answer 4

As detailed in the HTN response, by utilizing attr: keyof ListCount, you can refine the typings for the attr parameter. However, since ListCount contains properties with both string and number values, it is essential to verify if the attribute retrieved from b is of type number using typeof.

export class SumPipe implements PipeTransform {
  transform(items: ListCount[], attr: keyof ListCount): number {
    return items.reduce((a, b) => {
      // obtain the value of `attr` from `b`
      const value = b[attr];
      // check if the type of `b[attr]` is a number
      // - perform addition if true
      // - else, return the existing `a` value
      return typeof value === 'number' ? a += value : a;
    }, 0);
  }
}

Minimize the occurrence of errors by focusing on parameter piping transformations in Angular

Answer №1

Answer №2

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