Скачать или смотреть How to Properly Initialize an Empty NodeListOf in TypeScript

Struggling with TypeScript's `NodeListOf`? Discover how to correctly initialize an empty `NodeListOf` and alternative approaches, including using arrays for your DOM queries.
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This video is based on the question https://stackoverflow.com/q/68022289/ asked by the user 'michaelT' ( https://stackoverflow.com/u/9838670/ ) and on the answer https://stackoverflow.com/a/68023339/ provided by the user 'Alvin Leung' ( https://stackoverflow.com/u/16231108/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding NodeListOf Initialization in TypeScript

When you're working with TypeScript and trying to manipulate DOM elements, you might encounter challenges with generic types like NodeListOf. One common issue arises when attempting to initialize an empty NodeListOf and it becomes apparent that simply declaring an empty array won't suffice. If you're facing similar issues, you're not alone. In this guide, we will explore a practical approach to handling this scenario, ensuring your TypeScript code remains robust and functional.

The Problem: Initializing an Empty NodeListOf

Imagine you have a function designed to select multiple elements based on a specified query. Using the querySelector method works well, but you may run into trouble when you switch to querySelectorAll, especially when trying to initialize an empty variable of type NodeListOf.

Here’s an illustration of what you might initially try:

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When running the code above, TypeScript will throw an error stating: "The property 'item' is missing in type 'never[]' but required in type 'NodeListElement'". This indicates that you cannot directly assign an empty array to a NodeListOf type because they are inherently different types.

The Solution: Using Array.from

While there isn’t a built-in way to create an instance of NodeListOf without invoking querySelectorAll, you can use an alternative approach leveraging the flexibility of arrays, which can make your life easier. Here’s how:

Instead of directly trying to initialize a NodeListOf, you can work with a regular array and convert the NodeList results back into an array when needed. Here’s a step-by-step breakdown of the solution:

Step 1: Declare Your Buttons as an Array

Instead of declaring buttons as a NodeListOf, initialize it as a regular array of HTMLElement:

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Step 2: Utilize the selectorAll Function

Fetch the elements using your previously defined selectorAll function and convert the result into an array. This can be accomplished with Array.from:

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This approach creates an array that can easily be manipulated, which is often more convenient than working with a NodeList.

Final Implementation Example

Here’s a complete example that reflects the change from attempting to use a NodeListOf to utilizing an array:

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Conclusion

Handling NodeListOf in TypeScript can lead to frustrating hurdles, especially when initializing empty values. However, by opting for arrays instead and taking advantage of Array.from, you can achieve the desired functionality while avoiding compilation errors. This method not only sidesteps the pitfalls of type incompatibility but also enhances the ease of manipulating your selected elements.

Now you can confidently manage your DOM elements in TypeScript without running into type errors. Happy coding!