Before the optional chaining operator (?.) existed, it was sometimes troublesome to access deeply-nested properties in huge JavaScript objects when some of the intermediate properties might not be present.

const john = {
  profile: {
    name: { firstName: 'John', lastName: 'Doe' },
    age: 20,
    gender: 'Male',
  },
};

const jane = {
  profile: {
    age: 19,
    gender: 'Female',
  },
};

function getFirstName(user) {
  return user.profile.name.firstName;
}

Doing getFirstName(john) works but getFirstName(jane) will error because the name property doesn't exist for jane.profile.

Lodash's _.get method

Lodash's _.get method was created as a solution for such use cases.

Let's write our own version as a get function. The function gets the value at path of object. If the resolved value is undefined, the defaultValue is returned in its place. The function signature is as such:

get(object, path,[defaultValue]);

• object: The object to query.
• path: The path of the property to get.
  • It can be a single string with . as the separator between object fields (e.g. profile.name.firstName),
  • Or it can be an array like this: ['profile', 'name', 'firstName'].
• defaultValue: Optional parameter. The value returned if the resolved value is undefined. If defaultValue is not provided and the resolved value is undefined, simply return undefined.

Examples

// Using the `john` and `jane` objects from above
get(john, 'profile.name.firstName'); // 'John'
get(john, 'profile.gender'); // 'Male'
get(jane, 'profile.name.firstName'); // undefined

// An example where path is provided as an array
get({ a: { b: 2, c: { foo: 2 } } }, ['a', 'c']); // foo: 2,

Arrays inside the object can also be accessed if numerical indices are provided in the path. See the examples below.

get({a:[{b:{c:3}}]},'a.0.b.c');// 3
get({a:[{b:{c:3}}]},['a',0,'b','c']);// 3

There's no need to support mixed syntax of path such as get(object, 'a[0].b.c').

Editorial