Simple, standalone, vanilla implementation of lodash.get

deepGet.js

// Simple implementation of lodash.get
// Handles arrays, objects, and any nested combination of the two.
// Also handles undefined as a valid value - see test case for details.
// Based on: https://gist.github.com/harish2704/d0ee530e6ee75bad6fd30c98e5ad9dab
export function deepGet(obj, query, defaultVal) {
  query = Array.isArray(query) ? query : query.replace(/(\[(\d)\])/g, '.$2').replace(/^\./, '').split('.');
  if (!(query[0] in obj)) {
    return defaultVal;
  }
  obj = obj[query[0]];
  if (obj && query.length > 1) {
    return deepGet(obj, query.slice(1), defaultVal);
  }
  return obj;
}

deepGet.spec.js

import deepGet from './deepGet.js';

describe('deepGet', () => {
  const testObj = {
    a: {
      b: {
        c: {
          d: 123
        }
      },
      e: [
        { f: 9 },
        { g: 10 }
      ]
    }
  };

  const testArr = [
    { id: 1, comments: [{ text: 'hello' }, { text: 'goodbye' }] },
    { id: 2, comments: [] }
  ];

  const falseyObj = {
    isUndefined: undefined,
    isNull: null,
    isZero: 0,
    isEmptyString: ''
  };

  it('handles nested objects', () => {
    expect(deepGet(testObj, 'a.b.c.d')).toBe(123);
  });

  it('handles arrays inside an object', () => {
    expect(deepGet(testObj, 'a.e[0].f')).toBe(9);
  });

  it('handles objects inside an array', () => {
    expect(deepGet(testArr, '[0].comments[1].text')).toBe('goodbye');
  });

  it('returns the default value if query was not found', () => {
    const defaultVal = 'oh no';
    expect(deepGet(testObj, 'invalid.not[0].found', defaultVal)).toBe(defaultVal);
  });

  it('returns falsey values, including undefined', () => {
    const defaultVal = 'my default';
    expect(deepGet(falseyObj, 'isUndefined', defaultVal)).toBe(undefined);
    expect(deepGet(falseyObj, 'isNull', defaultVal)).toBe(null);
    expect(deepGet(falseyObj, 'isZero', defaultVal)).toBe(0);
    expect(deepGet(falseyObj, 'isEmptyString', defaultVal)).toBe('');
  });

});