Helper method to make `reduce(to(` be a somewhat awkard way to transform arrays to other types.

to.ts

export function to<A, T>(fn: (items: A[]) => T) {
  return (sum: any, _item: A, index: number, all: A[]): T => {
    const isLast = index === all.length - 1;

    if (!isLast) {
      return sum;
    }

    return fn(all);
  };
}
  
// Example

function join(items: string[]): string {
  return items.join('-');
}

['a', 'b', 'c'].reduce(to(join)); // 'a-b-c'

// Or, on the prototype

Array.prototype.chain = <T>(fn: (items: A[]) => T) {
  return this.reduce(to(fn));
}

['a', 'b', 'c'].chain(join); // 'a-b-c'