Convert an array to object utility in Typescript

Question

I have this utility function that given an array and the key by which it each item should be indexed, should convert it to an object:

export const convertArrayToObject = (array: any[], key: string): any => {
  const initialValue = {};
  return array.reduce((obj, item) => ({
    ...obj,
    [item[key]]: item,
  }), initialValue);
};

Here's what you should expect from this utility:

>>> console.log(convertArrayToObject(
  [
    {
      id: 'foo',
      color: 'blue'
    },
    {
      id: 'bar',
      color: 'red'
    }
  ], 'id'
));

This should log:

{
    foo: {
        id: 'foo',
        color: 'blue'
    },
    bar: {
        id: 'bar',
        color: 'red'
    }
}

The problem is, I'm using any twice and that breaks type safety for no good reason. I'm trying to write this utility function using generics but really finding it hard. Can someone help me replace the two anys with generics?

Soc · Accepted Answer · 2020-06-04 01:28:15Z

1

You should be able to do this with generics. Example:

function convertArrayToObject<T extends {[key: string]: any}>(array: T[], key: string): {[key: string]: T} {
  const obj: {[key: string]: T} = {};
  array.forEach(item => {
    obj[item[key]] = item
  });

  return obj;
}

console.log(convertArrayToObject(
  [
    {
      id: 'foo',
      color: 'blue'
    },
    {
      id: 'bar',
      color: 'red'
    }
  ], 'id'
));

Alternatively, you could use Object.fromEntries combined with map:

const obj = Object.fromEntries([
  {
    id: 'foo',
    color: 'blue'
  },
  {
    id: 'bar',
    color: 'red'
  }
].map(item => [item.id, item]));

console.log(obj);

answered Jun 4, 2020 at 1:28

Soc

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