JavaScript › Classes & Class Syntax

Why can classes not be called without 'new', unlike regular functions?

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Answer

Class constructors are designed to enforce proper object construction; calling a class without new throws a TypeError by specification, unlike ordinary functions which silently run with 'this' bound to undefined (in strict mode) or the global object.

class Foo {}
Foo(); // TypeError: Class constructor Foo cannot be invoked without 'new'

Real-world example Preventing a common bug where a class is accidentally called like a plain function and silently misbehaves.

Common follow-ups: How do factory functions differ from classes in this respect?

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