The new.target property lets you detect whether a function or constructor was called using the new operator.
function Foo() {
if (!new.target) throw 'Foo() must be called with new';
console.log('Foo instantiated with new');
}
new Foo(); // logs "Foo instantiated with new"
Foo(); // throws "Foo() must be called with new"
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new.target