class constructor mongostore cannot be invoked without new

In this article, we will be handling the typeerror: class constructor mongostore cannot be invoked without new.

By the time you finish reading this article, you should be able to identify the cause of this error and apply the proper fixes.

Let us not prolong our introduction and proceed to understand this error.

What is typeerror: class constructor mongostore cannot be invoked without new?

The typeerror: class constructor mongostore cannot be invoked without new is an error message that appears in JavaScript.

The error mentioned above indicates that the issue is in the way we call the class constructor mongostore.

It specified that without using the keyword “new,” the constructor could not be invoked.

What are constructor functions?

Constructor functions are functions in JavaScript.

They are used to generate objects with a particular set of properties and methods.

These can’t be invoked without the keyword “new,” because this keyword is used to create a new instance of the object.

For this error to occur, you might have forgotten to add the “new” keyword when calling the constructor function for the MongoStore class.

Here is a sample code that triggers this error:

const session = require('express-session');
const MongoStore = require('connect-mongo')(session);

const store = MongoStore({
    url: 'mongodb://localhost:27017/myapp',
    ttl: 60 * 60 // session expiration time in seconds
});

app.use(session({
    secret: 'mysecret',
    resave: false,
    saveUninitialized: false,
    store: store
}));

Typeerror: class constructor mongostore cannot be invoked without new – SOLUTION

Complete code:

const session = require('express-session');
const MongoStore = require('connect-mongo')(session);

const store = new MongoStore({
  url: 'mongodb://localhost:27017/myapp',
  ttl: 60 * 60 // session expiration time in seconds
});

app.use(session({
  secret: 'mysecret',
  resave: false,
  saveUninitialized: false,
  store: store
}));

See also: Typeerror: class constructor servecommand cannot be invoked without ‘new’

FAQs

Understanding int/str/float TypeErrors

Python separates numeric types from strings strictly. Concatenating, comparing, and arithmetic across type boundaries requires explicit conversion.

Common triggers

• User input is always str. input() always returns str. Wrap with int() or float().
• CSV cells are all str. Even numeric-looking columns are strings until converted.
• JSON numbers vs str. json.loads preserves the JSON type — but only “123” as string in the JSON becomes str in Python.
• Format string mismatch. "%d" % "5" raises TypeError. Use int("5") first.
• Compare int and str. Python 3 fails on "1" < 2. Convert one side first.

Diagnostic pattern

# BAD — user input treated as int
age = input("Enter your age: ")
if age >= 18:  # TypeError: '>=' not supported between 'str' and 'int'
    print("Adult")

# GOOD — convert first, guard failure
try:
    age = int(input("Enter your age: "))
except ValueError:
    print("Invalid age")
    age = 0

if age >= 18:
    print("Adult")

Best practices

• Convert at boundaries. Convert input, config values, and API responses to the right type immediately after loading.
• Use pydantic or dataclasses. Modern data validation libraries convert and check types automatically.
• Avoid == across types. Compare like-to-like.

Conclusion

In conclusion, the typeerror: class constructor mongostore cannot be invoked without new is encountered in JavaScript.

You can fix this error by making sure that you are using the “new” keyword when calling the constructor function for the MongoStore class.

By following the guide above, you will surely solve this error quickly.

That is all for this tutorial, IT source coders!

We hope you have learned a lot from this. Have fun coding!

Thank you for reading! 😊

Elijah Galero

Programmer & Technical Writer at PIES IT Solution

Elijah Galero is a programmer and writer at PIES IT Solution, author of 175+ tutorials at itsourcecode.com. Specializes in Python error debugging (AttributeError, TypeError, ModuleNotFoundError), Python programming tutorials, and Microsoft Excel how-to guides for BSIT students and productivity learners.

Expertise: Python · Python Errors · Python AttributeError · Python TypeError · ModuleNotFoundError · MS Excel · MS PowerPoint
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