Type '(e: React.ChangeEvent<HTMLInputElement>) => void' is not assignable to type 'FormEventHandler<HTMLFormElement>'. Types of parameters 'e' and 'event' are incompatible.

Understanding TypeScript Error: Type '(e: React.ChangeEvent<HTMLInputElement>) => void' is not assignable to type 'FormEventHandler<HTMLFormElement>'. Types of parameters 'e' and 'event' are incompatible.#

As a web developer, I have come across this error message multiple times while working with TypeScript. This error is related to the type of event handlers in TypeScript. In this blog post, I will try to explain what this error means and how to fix it.

What's the problem?#

The error message is quite clear in stating that there is a type mismatch between two types of event handlers: '(e: React.ChangeEvent<HTMLInputElement>) => void' and 'FormEventHandler<HTMLFormElement>'.

Let's break down these two types:

• '(e: React.ChangeEvent<HTMLInputElement>) => void': This is a type of event handler that takes an argument of type 'React.ChangeEvent<HTMLInputElement>' and returns nothing.
• 'FormEventHandler<HTMLFormElement>': This is a type of event handler that takes an argument of type 'Event' and returns nothing. The argument is expected to be an event that occurs on a 'form' element.

The error message is stating that these two types are not compatible because the argument expected for the first type, 'React.ChangeEvent<HTMLInputElement>', is more specific than the argument expected for the second type, 'Event'.

How to fix it?#

To fix this error, we need to make sure that the argument type for our event handler matches the type expected by the 'FormEventHandler<HTMLFormElement>' type.

One way to do this is to change the type of our event handler to 'FormEventHandler<HTMLFormElement>'. Here's an example:

const handleSubmit: FormEventHandler<HTMLFormElement> = (event) => {
  event.preventDefault();
  // rest of the code
}

In this code, we changed the type of our event handler 'handleSubmit' to 'FormEventHandler<HTMLFormElement>'. This ensures that our event handler function takes an argument of type 'Event' which is expected by the 'FormEventHandler' type.

Another way to fix this error is to change the type of our event handler to '(e: React.FormEvent<HTMLFormElement>) => void'. Here's an example:

const handleSubmit = (event: React.FormEvent<HTMLFormElement>) => {
  event.preventDefault();
  // rest of the code
}

In this code, we changed the type of our event handler 'handleSubmit' to '(e: React.FormEvent<HTMLFormElement>) => void'. This ensures that our event handler function takes an argument of type 'React.FormEvent<HTMLFormElement>' which is equivalent to the 'FormEventHandler' type.

Conclusion#

TypeScript is a great tool for catching errors in our code before it even runs. In this blog post, we learned about one such error related to the type of event handlers. We also learned two ways to fix this error. By understanding and fixing these errors, we can write better and more robust code.