Common JavaScript Errors and How to Fix Them
Browse all documented JavaScript errors with detailed explanations, root causes, and step-by-step fixes.
Invalid hook 'useEffect' hook invocation: Missing dependency on 'fetchData' func
This error occurs when the 'useEffect' hook is invoked without specifying its dependencies, which can lead to unexpected…
Template is not a function. Got function for type: 'object'
This error occurs when a template function in a framework like React or Vue is called incorrectly. It happens when a com…
Unexpected token 'class' in JSON at position 0
This error occurs when the JavaScript interpreter is expecting a JSON object but encounters a class definition instead, …
SyntaxError: Unexpected token 'let' in JSON at position 1
This error occurs when the JavaScript interpreter encounters a syntax that is not valid JSON. In this case, it's due to …
Error: Unable to resolve dependency 'http-proxy-middleware' in /node_modules/rea
This error occurs when the dependencies of a project are not properly configured, and the framework is unable to resolve…
Error: ECONNRESET: Connection was reset
This error occurs when a connection to a database or a server is unexpectedly dropped. It can be caused by a network iss…
Unexpected token ILLEGAL, expected }
This error occurs when the JavaScript interpreter encounters an invalid or unexpected token in the code. In this case, i…
Error: Cannot find module 'express-validator' imported from /path/to/app.js
This error occurs when a JavaScript module or package is not found by the framework's module resolver, often due to a ty…
MongoDB driver assertion error: TypeError: Cannot read properties of undefined (
This error occurs when there's an issue with the MongoDB driver or the database connection, often due to a mismatch betw…
Cannot access 'Promise' prototype's method 'then' on 'undefined' because it is a
This error occurs when trying to call a method on a non-function value, in this case, a Promise that is pending or rejec…
Uncaught Error: Route not found: /users/:id
This error occurs when the router in a JavaScript framework (e.g., Express.js, Next.js) fails to find a matching route f…
ReferenceError: Cannot access 'length' property on 'NaN' (while parsing at 'inpu
This error occurs when trying to access a property (like 'length') on a value that is not an object.…
Have a JavaScript error that's not listed? Get an instant explanation.
Explain Another Error