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Javascript – How to return string[]?

my question is – how return a string[]. Right now TS throw error because every element of array is type of ( T[keyof T] extends readonly (infer InnerArr)[] ? InnerArr : T[keyof T] )
How do i accept ‘property’ argument as a string for return string[]. If i just write string instead keyof T, TS throw error because on the line item[property] TS can’t see propert in unknown type.

interface IMovie {
  genre: string[];
  actors: string[];
}

const movies: IMovie[] = [
  {
    genre: ['Action', 'Sci-Fi', 'Adventure'],
    actors: ['Scarlett Johansson', 'Florence Pugh', 'David Harbour'],
  }
];

function collectByProperty<T>(arr: T[], property: keyof T): string[] {
  const array = arr.map((item) => item[property]).flat();
  const elem = array[0];
  const final = [...new Set(array)];
  return final;
}
const genres = collectByProperty<IMovie>(movies, 'genre');
const actors = collectByProperty<IMovie>(movies, 'actors');

console.log(genres);
console.log(actors);

Tried to create variable in function body and write in it property.

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2

Answers


  1. 0

    Use flatMap instead of map then flat:

    const array = arr.flatMap((item) => item[property]);
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  2. 0

    You need to flatten the array in your collectByProperty function because it initially produces an array of arrays (like [['Action', 'Sci-Fi'], ['Drama']]). Flattening this converts it into a single-level array (['Action', 'Sci-Fi', 'Drama']), matching the expected output.

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