Understanding the Error: Argument of type ‘HTMLElement | null’ is not assignable to parameter of type ‘Element’
If you are working with React and TypeScript, you may have come across the error message “Argument of type ‘HTMLElement | null’ is not assignable to parameter of type ‘Element’. Type ‘null’ is not assignable to type ‘Element’.” This error often occurs when you try to assign a value returned from document.getElementById to a variable.
Why does this error occur?
The error occurs because document.getElementById returns an HTMLElement | null. This means that it can either return an HTMLElement if an element with the specified ID is found, or it can return null if no matching element is found.
Solution 1: Using a Non-null Assertion Operator
One way to handle this error is by using a non-null assertion operator (!) to assert that the value is never null. This operator tells TypeScript that you are certain the value will not be null, even though the type allows it.
const portalDiv = document.getElementById('your-element')!;By appending the ! operator at the end of the statement, you are informing TypeScript that the value returned by getElementById should be treated as an HTMLElement and not null.
Solution 2: Casting the Element
Another approach to eliminate the error is by explicitly casting the element using the as keyword. This lets TypeScript know that you are confident the value is of type HTMLElement.
const portalDiv = document.getElementById('portal') as HTMLElement;By using the as HTMLElement syntax, you are informing TypeScript that the result of getElementById should be treated as an HTMLElement.
Solution 3: Conditional Rendering
If you prefer to avoid non-null assertions or type casting, you can also use conditional rendering to handle the possibility of the element being null. This approach allows you to conditionally render components based on whether the element exists or not.
const portalDiv = document.getElementById('portal');
if (portalDiv) {
return ReactDOM.createPortal(
<div>
{props.children}
<div/>
, portalDiv);
}
return null;In the above code, we first check if the portalDiv element exists using the condition if (portalDiv). If it exists, we render the component inside the portal using ReactDOM.createPortal. If it does not exist, we return null or any suitable fallback UI.
Conclusion
The error “Argument of type ‘HTMLElement | null’ is not assignable to parameter of type ‘Element’. Type ‘null’ is not assignable to type ‘Element'” is commonly encountered when working with React and TypeScript. By using non-null assertions, type casting, or conditional rendering, you can overcome this error and ensure smooth execution of your code.
Remember to choose the solution that best suits your preferences and use it consistently throughout your codebase. Happy coding!
