Скачать или смотреть Resolving the TypeScript Issue with ReactDOM.createPortal and document.getElementById

Discover how to handle the TypeScript error in React when using createPortal and document.getElementById. Learn simple solutions to enhance your development workflow.
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This video is based on the question https://stackoverflow.com/q/69007457/ asked by the user 'Connor Mooneyhan' ( https://stackoverflow.com/u/4592937/ ) and on the answer https://stackoverflow.com/a/69007486/ provided by the user 'Michael Lorton' ( https://stackoverflow.com/u/238884/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the TypeScript Issue with ReactDOM.createPortal

If you're a developer using TypeScript with React, you may have encountered some challenging type-checking issues, particularly when using ReactDOM.createPortal. One common problem arises when you try to get an element from the DOM using document.getElementById, only to find that TypeScript throws an error. This post aims to unravel the mystery behind this issue and provide you with a straightforward solution.

The Problem

In the provided code, you're trying to create a portal for a modal using React:

[[See Video to Reveal this Text or Code Snippet]]

When you run this code, TypeScript complains with the following error message when you hover over document.getElementById('overlay-root'):

[[See Video to Reveal this Text or Code Snippet]]

This error occurs because TypeScript cannot guarantee that the element returned by document.getElementById is not null. In pure JavaScript, this function might work seamlessly, but TypeScript requires strict type checking, which leads to the error you're facing.

Breakdown of the Solution

The issue stems from the fact that TypeScript evaluates the possibility of getElementById returning null, especially if the HTML element with the specified ID does not exist in the DOM at the time of calling. To resolve this, we need to convey to TypeScript that we are confident the value is not null. Here's how to do it:

1. Use Non-null Assertion Operator

You can assert to TypeScript that the value returned from getElementById is indeed not null by using the non-null assertion operator !. Here's how you can update your code:

[[See Video to Reveal this Text or Code Snippet]]

By appending !, you tell TypeScript that document.getElementById('overlay-root') will not be null, and it can treat it as an Element type.

2. Be Cautious with Runtime Errors

While this approach effectively resolves the type error, you should be cautious. Asserting that the value is non-null could lead to a runtime error if your assumption is inaccurate — if the overlay-root element does not exist in the DOM, your application will crash. Therefore, you might want to handle this more gracefully:

Example of Safe Handling

Instead of using the non-null assertion directly, you could check if the element exists:

[[See Video to Reveal this Text or Code Snippet]]

This way, you ensure that your application won't run into errors due to null values, making it safer and more robust.

Conclusion

The TypeScript issue with document.getElementById in the context of using ReactDOM.createPortal can be resolved through proper handling of potential null values. By using the non-null assertion operator or implementing checks for element existence, you can code effectively without type errors. Always remember to be cautious when making assertions, as runtime errors can lead to a poor user experience.

With this knowledge in hand, you're well-equipped to navigate similar issues in your React and TypeScript projects. Happy coding!