Originally published on php-to-js.learnio.dev — part of the PHP to JavaScript course. View this lesson on the original site.

Safe defaults without throwing on nested data

PHP 7.4 gave you ??. PHP 8 gave you ?->. JavaScript has the same pair: ?? for nullish defaults and ?. for optional chaining. Together they replace long isset chains.

PHP habit: null coalescing

<?php
$user = null;
$name = $user ?? 'Guest';

$count = 0;
// || would be wrong if 0 is valid:
// $display = $count || 10;

$display = $count ?? 10;  // 0 — only null/undefined trigger ?? in JS; in PHP ?? is null-only

Note: in PHP ?? only checks null (and undefined variable notices). In JavaScript ?? checks null and undefined.

JavaScript equivalent

const user = null;
const name = user ?? 'Guest';

const count = 0;
console.log(count || 10);  // 10 — 0 is falsy
console.log(count ?? 10);  // 0  — 0 is not nullish
Expression When right-hand side runs
|| / && When left is falsy / truthy
?? When left is null or undefined only

PHP habit: nullsafe operator

<?php
$city = $user?->address?->city ?? 'Unknown';

JavaScript equivalent

const city = user?.address?.city ?? 'Unknown';
PHP JavaScript
$user?->address user?.address
?? 'Unknown' ?? 'Unknown'

Three forms of ?.

obj?.prop;      // property
arr?.[0];       // index
callback?.();   // call only if function exists

Mapping from isset chains

<?php
$city = isset($user['address']['city'])
    ? $user['address']['city']
    : 'Unknown';

const city = user?.address?.city ?? 'Unknown';

Shorter to read and no risk of notices when an intermediate key is missing.

Try it

Use the amber Try it panel below. Click Run.

const user = { address: { city: 'Leeds' } };
const missing = null;

console.log(user?.address?.city ?? 'Unknown');
console.log(missing?.address?.city ?? 'Unknown');

const count = 0;
console.log('with ||', count || 10);
console.log('with ??', count ?? 10);

You should see Leeds, then Unknown, then 10 and 0. That 0 line is why ?? matters for API and form defaults.

From PHP to JavaScript — JavaScript Syntax Foundations for PHP Devs