SyntaxError: Invalid optional chain from new expression (V8-based)SyntaxError: new keyword cannot be used with an optional chain (Firefox)SyntaxError: Cannot call constructor in an optional chain. (Safari)

There are two ways to get this error. The first one is if the constructor expression is an optional chain expression, like this:

new Intl?.DateTimeFormat();Number?.[parseMethod]`Hello, world!`;

The second one is if?. occurs between the constructor and the arguments list, like this:

new Intl.DateTimeFormat?.();

Optionalnew is specifically forbidden because its syntax is complicated (new with and without arguments), and the result is unclear (it would be the only case wherenew does not evaluate to an object value). You need to translate the optional chaining to its underlying condition (seeoptional chaining for more information).

const result =  Intl.DateTimeFormat === null || Intl.DateTimeFormat === undefined    ? undefined    : new Intl.DateTimeFormat();

Remember that optional chaining only short-circuits within a parenthesized unit. If you parenthesize your constructor expression, the optional chaining will not cause an error, because now the constructor does not short-circuit and the result is clear (the constructor will produceundefined and then cause thenew expression to throw).

new (Intl?.DateTimeFormat)(); // Throws if Intl?.DateTimeFormat is undefined

However this is a bit nonsensical anyway because optional chaining prevents errors inside the property access chain, but is then guaranteed to generate an error when callingnew. You would probably still want to use a conditional check.

Note that optional chaining is only forbidden as the constructor expression. You can use optional chaining inside the argument list, or use optional chaining on thenew expression as a whole.

new Intl.DateTimeFormat(navigator?.languages);new Intl.DateTimeFormat().resolvedOptions?.();

Note that there's no needs to use?. on thenew expression itself:new a()?.b, becausenew is guaranteed to produce a non-nullish object value.

• new
• Optional chaining (?.)
• Original discussion on whether "optional new" should be allowed