insert.test.ts

import { insert } from './insert';

const input = [
  {
    priority: 20
  }
];

test('Should return array with one element when empty', () => {
  const result = insert([], { priority: 2 }, 'priority');
  expect(result).toEqual([{ priority: 2 }]);
});

test('Should add one element everytime its called', () => {
  let result = insert([], { priority: 10 }, 'priority');
  expect(result.length).toBe(1);

  result = insert(result, { priority: 5 }, 'priority');
  expect(result.length).toBe(2);

  result = insert(result, { priority: 0 }, 'priority');
  expect(result.length).toBe(3);

  result = insert(result, { priority: 20 }, 'priority');
  expect(result.length).toBe(4);
});

test('Should return array ordered by property', () => {
  let result = insert(input, { priority: 40 }, 'priority');
  expect(result).toEqual([{ priority: 40 }, ...input]);

  result = insert(input, { priority: 0 }, 'priority');
  expect(result).toEqual([...input, { priority: 0 }]);

  result = insert(input, { priority: 0 }, 'priority');
  expect(result).toEqual([...input, { priority: 0 }]);
});

test('Should add element at the start if priority is higher', () => {
  let result = insert(input, { priority: 21 }, 'priority');
  expect(result).toEqual([{ priority: 21 }, ...input]);
});

test('Should add element at the end if priority is lower', () => {
  let result = insert(input, { priority: 5 }, 'priority');
  expect(result).toEqual([...input, { priority: 5 }]);
});

insert.ts

/**
 * Take a List of Objects and insert at
 * the desired index based on the property
 * @param array arr
 * @param Object valToInsert
 * @param string {property} Object property
 * @returns {}
 */
export const insert = <T>(arr: Array<T>, valToInsert: T, property: string): Array<T> => {
  let result: Array<T> = new Array(...arr) || [];

  if (arr.length === 0) return [valToInsert];

  for (let i = 0; i < arr.length; i++) {
    if (valToInsert[property] >= arr[i][property]) {
      result.splice(i, 0, valToInsert);
      break;
    }

    if (valToInsert[property] < arr[i][property] && i + 1 === arr.length) {
      result.push(valToInsert);
      break;
    }
  }

  return result;
};