---
title: "Elvis Operator"
url: "https://www.bekk.christmas/post/2018/03/elvis-operator"
authors: ["Henrik Hermansen"]
published: "2018-12-03"
updated: "2024-11-07T13:05:28Z"
language: "en-US"
type: "article"
tags: ["JavaScript"]
---

# Elvis Operator

How to rock and roll with Optional Chaining

## In short

Optional chaining (`?.`) lets JavaScript safely walk through nested properties without throwing a `TypeError` when an intermediate value is `undefined`. It can also be used for function calls and array access, but each step only checks the current link in the chain, so there are some gotchas and it can still fail if something isn’t the right kind of value.

- **For:** JavaScript developers
- **Good to know beforehand:** Basic JavaScript and undefined checks

_AI-generated_

# Elvis ~~Presley~~ Operator

Are you being a responsible developer and _rocking_ your undefined-checks to prevent [TypeError](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError) like this?

```js
const street = customer && customer.address && customer.address.street;
```

That's nice, but you may have noticed it doesn't _roll_ very well. While it's great to protect yourself from type errors, it can get tedious and cumbersome, and it doesn't feel very [DRY](https://en.wikipedia.org/wiki/Don%27t_repeat_yourself).

I hope this won't leave you all shook up. Instead, you should read on - it's now or never!

## Rock _and_ roll 🕺

As you learned on [Day 1](https://javascript.christmas/2018/1) JavaScript is always open for suggested features and additions. One of these suggestions is called "[Optional Chaining](https://github.com/tc39/proposal-optional-chaining)", and is about the operator best known as the [Elvis operator](https://en.wikipedia.org/wiki/Elvis_operator).

The suggested operator looks like this `?.`, and you can use it to _chain_ undefined-checks:

```js
const street = customer?.address?.street;
```

This will check if both `customer` and `address` is present, and give you the value of `street`. However, if `customer` does not have the property `address`, or if `customer.address` does not have the property `street`, your variable will receive the value `undefined`, and no type errors are thrown.

You can even use this to safely (kinda) run functions or access items in an array:

```js
customers?.[2];
api?.getCustomer?.();
```

This will make sure both `api` and `api.getCustomer` is present, before trying to run `getCustomer`. Beware though, that this will still throw a type error if `getCustomer` is [not a function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_function).

### Could I go wrong with this?

Yes, there are some limitations and gotchas to this feature.

The biggest pitfall might be that each operator will only check the current link in the chain:

```js
customer?.address.street; // will throw an error if address is undefined
customer.address?.street; // will throw an error if customer is undefined
```

For more details I suggest you have a closer look at [~~The Proposal~~](https://www.imdb.com/title/tt1041829/)[the proposal](https://github.com/tc39/proposal-optional-chaining).

### Awesome! When can I use it?

Now! While the feature is currently in _stage 1_, it is of course available as a [babel plugin](https://www.npmjs.com/package/@babel/plugin-proposal-optional-chaining).

I don't know about you, but I just can't help falling in love.

## Relevant resources recommended by the author

- [TC39 proposal](https://github.com/tc39/proposal-optional-chaining)
- [Babel plugin](https://www.npmjs.com/package/@babel/plugin-proposal-optional-chaining)

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