sort keys of an object using an array index as rank, with TypeScript

sort-object-keys.ts

export interface SomeShape {
  b: string,
  c: string,
  a: string,
}

// Specify your sort order here
const rank: Array<keyof SomeShape> = ['a', 'b', 'c'];

export function sortedKvpString(obj: SomeShape) {
  return Object.entries(obj)
    .sort(([a_], [b_]) => {
      const a = a_ as keyof SomeShape; // #ts workaround :.(
      const b = b_ as keyof SomeShape;
      return rank.indexOf(a) - rank.indexOf(b);
    })
    .map(([key, val])=> `* ${key}: ${val}`)
    .join('\n');
}

// Now we know they'll print in order:
console.log(
  sortedKvpString({b: 3, a: 1, c: 5}) // prints a,b,c
);