How to transform an Array nested in an Object?

Question

I'm stuck with compile errors while trying to to convert an Object that contains an Array of Objects.

That's what's coming in:

export interface CourseRaw {
  metaInfo: MetaInfoRaw;
  gameCode: number;
  gameText: string;
  images?: ImageRaw[]; // Problems here
}

export interface ImageRaw {
  uploaded: string;
  url?: string;
  description?: string;
  fileName?: string;
}

The output shall be typed objects (interfaces) I have left out many properties here for better reading, hence the "Course" object would look the same as the "CourseRaw" object except for the type "Image[]". Notice that "Image" contains "uploaded" as Date rather than string as seen in "ImageRaw"

export interface Image {
  uploaded: Date;
  url?: string;
  description?: string;
  fileName?: string;
}

In the transforming function I tried to copy the data into a new array, which the compiler doesn't accept:

export class CourseFactory {    
  static fromRaw(courseRaw: CourseRaw): Course {
    return {
      ...courseRaw,      
      ratingInfo: RatingFactory.fromRaw(courseRaw.ratingInfo), // demo of another nested object (works)
      images: ImageFactory.fromRaw(courseRaw.images) // problematic call
    };
  }

My attempt to actually copy the data (failed):

   static fromRaw(imageRaw: ImageRaw[]): Image[] {
    var newImages;

    var i;
    for (i = 0; i < imageRaw.length; i++) {
      newImages[i].uploaded = new Date(imageRaw[i].uploaded);
      newImages[i].url = imageRaw[i].url;
      newImages[i].description = imageRaw[i].description;
      newImages[i].fileName = imageRaw[i].fileName;
    }
    return newImages;
  }

How can I make it right?

score 0 · Accepted Answer · answered Apr 28 '20 at 10:14

You should type the Image return array. Furthermore you can add a map to to do it easily.

static fromRaw(imageRaws: ImageRaw[]): Image[] {
  return imageRaws.map(raw => {
    return {
      uploaded: new Date(...),
      url: raw.url,
      // etc.
    }
  });
}

Since array creation is in the return instruction, TS should get the typings right.

About your code:

You can make it work adding var newImages: Image[] = []; (initialization and type definition)
You should use push to add new items to the array; if you really want to initialize array length (see related question/answer ), you should add newImages.length = imageRaws.length.

How to transform an Array nested in an Object?

1 Answers1