```ts
export function fieldOf(record: Record<string, number>, field: string): number {
  if (!record.hasOwnProperty(field)) {
    throw new Error(`Record lacks field ${field}`);
  }
  return record[field];
}

export function sortPairs(records: Record<string, number>[], field: string): Record<string, number>[] {
  return records.sort((a, b) => a[field] - b[field]);
}
```