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Explain 'Not a constructor function' error in JavaScript?
The "Not a constructor function" error occurs when we try to use the new keyword with a value that isn't a constructor function. This TypeError is thrown when JavaScript expects a constructor but receives a primitive value, object, or non-constructor function.
What Causes This Error
The error occurs when we attempt to instantiate something that cannot be used as a constructor:
- Primitive values (numbers, strings, booleans)
- Regular objects
- Arrow functions (in strict mode)
- Built-in methods that aren't constructors
Example: Using Primitive as Constructor
Constructor Error Demo
Common Scenarios and Solutions
Constructor Solutions
How to Fix This Error
| Problem | Solution | Example |
|---|---|---|
Using primitive with new
|
Use constructor function or class |
new String("text") instead of new "text"
|
Using object with new
|
Create constructor function | function MyObj() {} |
| Using arrow function | Use regular function or class | function MyFunc() {} |
Prevention Tips
Conclusion
The "Not a constructor function" error occurs when using new with non-constructor values. Always ensure you're using constructor functions, classes, or built-in constructors like Array, Object, or Date with the new keyword.
Updated on: 2026-03-15T23:18:59+05:30
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