Inject extra properties into a native interface

array_injection.ts

// Defining a searchBy method on an array
interface SearchFn<T> {
  (key: string, value: string): { index: number; value: T }[] | undefined;
}

// Extend the Array interface to include a searchBy method
interface SearchableArray<T> extends Array<T> {
  searchBy: SearchFn<T>;
}

// Inject the searchBy method into an array
const injectSearch = <T>(array: T[]): SearchableArray<T> => {
  Object.defineProperties(array, {
    searchBy: {
      value: function (this: T[], key: string, value: string) {
        return this.reduce(
          (previous, current: any, index) => {
            if (current && current[key] && current[key] === value) {
              previous.push({ index, value: current });
            }

            return previous;
          },
          [] as { index: number; value: T }[],
        );
      } as SearchFn<T>,
    },
  });

  return array as SearchableArray<T>;
};

// Definition of a Person object
interface Person {
  firstName: string;
  lastName: string;
  age: number;
}

// Creating an array of people that can be searched
const people = injectSearch<Person>([]);

people.push({
  age: 20,
  firstName: 'John',
  lastName: 'Doe',
});

people.push({
  age: 75,
  firstName: 'Jane',
  lastName: 'Doe',
});

const john = people.searchBy('firstName', 'John');
console.log('John:', john);

const jane = people.searchBy('firstName', 'Jane');
console.log('Jane:', jane);

const all = people.searchBy('lastName', 'Doe');
console.log('All:', all);

/**
John: [
  { index: 0, value: { age: 20, firstName: 'John', lastName: 'Doe' } }
]
Jane: [
  { index: 1, value: { age: 75, firstName: 'Jane', lastName: 'Doe' } }
]
All: [
  { index: 0, value: { age: 20, firstName: 'John', lastName: 'Doe' } },
  { index: 1, value: { age: 75, firstName: 'Jane', lastName: 'Doe' } }
]
*/