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JavaScript class constructor was called without new

TypeError: class constructors must be invoked with 'new'

JavaScript tried to call a class constructor like a normal function instead of instantiating it with new.

TypeError: class constructors must be invoked with 'new'runtime

Observed message

TypeError: class constructors must be invoked with 'new'

Why it happens

  • A class is being invoked like a regular function.
  • A value expected to be a factory function is actually a class.
  • A refactor changed a callable API into a class-based one.

How to fix it

  1. Instantiate the class with new.
  2. Check whether the imported value is a class or a factory function.
  3. Update wrappers and call sites to match the class-based API.

Official reference

MDN: TypeError: class constructors must be invoked with new

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