Generic type ascertaining a key is present in the type

Question

Given this minimal example

interface Sorting {
  myValue: number
}

const mySort = (data: Sorting[]) => {
  data.sort((a: Sorting, b: Sorting) => {
    return a.myValue - b.myValue
  })
  return data
}

I would like to create some code that abstracts the myValue property, such that I could type safely write something as below

interface Sorting {
  [key]: number
}

const mySort = (data: Sorting[], [key]: "myValue") => {
  data.sort((a: Sorting, b: Sorting) => {
    return a[key] - b[key]
  })
  return data
}

Answer 1

You can make your sort function generic, and express the relation between the object type and the sort key in the generic type parameters:

const mySort = <
  T extends { [k in K]: number },
  K extends keyof T
>(data: T[], key: K) => {
  data.sort((a: T, b: T) => {
    return a[key] - b[key];
  })
  return data;
};

const data = mySort([{ myValue: 2 }, { myValue: 1 }], 'myValue');
console.log(data);

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^{Playground link}

Now you can pass an array of any type to the sort function, as long as the key you're specifying corresponds to a numeric property of that type.