Optional Chaining for JavaScript

October 14, 2020

Introduced in ES2020, the optional chaining operator, allows for a simple way to check the value of a deeply nested property within chained objects. Traditionally in JavaScript, getting the value of a deeply-nested property meant validating each reference in the chain.

const user = {
  name: 'Cosmo Kramer',
  address: {
    home: {
      street: '129 West 81st St.',
      unit: '5B',
      city: 'New York',
      state: 'NY',
      zip_code: '10024',
    },
  },
};

const homeZipCode =
  user.address && user.address.home && user.address.home.zip_code;
// '109024'

const workZipCode =
  user.address && user.address.work && user.address.work.zip_code;
// udefined

If the reference to a value deep within a chain of nested objects is null or undefined, it will throw a TypeError.

const workZip = user.address.work.zip_code;
// throws a TypeError since `user.address.work` is undefined

The Optional Chaining Operator

The optional chaining operator (?.) allows us to simplify our expression when chained properties may be nullish (null or undefined). If the value preceding the optional chaining operator is null or undefined, the expression short-circuits and returns undefined.

const homeZipCode = user.address?.home?.zip_code; // '10024'
const workZipCode = user.address?.work?.zip_code; // undefined

Handling Defaults

The nullish coalescing operator (??) can handle instances where a value other than undefined is desired for the nullish reference.

const workZipCode = user.address?.work?.zip_code ?? 'N/A';