What is the process of converting an Array that is nested within an Object?

I am facing compile errors while attempting to convert an Object containing an Array of Objects.

Here is the initial structure:

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

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

The desired outcome should be typed objects (interfaces) with some properties omitted for clarity, notably changing the type of "Image" from "ImageRaw". Note that "Image" now includes "uploaded" as a Date instead of a string as in "ImageRaw"

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

In my transformation function, I attempted to duplicate the data into a new array, but encountered compiler errors:

export class CourseFactory {    
  static fromRaw(courseRaw: CourseRaw): Course {
    return {
      ...courseRaw,      
      ratingInfo: RatingFactory.fromRaw(courseRaw.ratingInfo), // Nested object example (successful)
      images: ImageFactory.fromRaw(courseRaw.images) // Issue arises here
    };
  }

My failed attempt at copying the data:

   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 resolve this issue?

Answer №1

To easily create an array of images, you can implement a function that takes an array of raw image data and returns an array of Image objects. To make it more efficient, consider using a map function.

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

TypeScript should infer the correct typings based on the return value of the function where the array is created.

Tips for optimizing your code:

  1. Initialize and define the type for the new array before adding elements: var newImages: Image[] = [];
  2. When adding items to the array, use the push method instead of trying to set the length of the array initially. If setting the length is necessary, you can do so after initializing the array with
    newImages.length = imageRaws.length
    .

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