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Learn how to easily convert TypeScript syntax to JSDoc for better JavaScript compatibility. Follow our step-by-step guide.
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This video is based on the question https://stackoverflow.com/q/76831857/ asked by the user 'petercli' ( https://stackoverflow.com/u/8107515/ ) and on the answer https://stackoverflow.com/a/76832922/ provided by the user 'brunnerh' ( https://stackoverflow.com/u/546730/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Converting TypeScript Syntax to JSDoc: A Simple Guide

In the world of coding, developers often find themselves needing to convert TypeScript (TS) syntax into plain JavaScript with JSDoc annotations. This conversion can be necessary for various reasons, such as compatibility with existing JavaScript codebases or libraries. If you're encountering issues with the conversion process or need guidance on how to properly implement JSDoc, you're in the right place. Let's dive into the solution with a clear breakdown of the process.

Understanding the Problem

As a practical example, consider the following TypeScript snippet that needs to be converted into JavaScript with JSDoc annotations:

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When converting it, one might run into errors, such as "unexpected token" when trying to reference types or variables that exist only in TypeScript. Below is the expected output after conversion:

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Common Errors

Here's a snippet that indicates a common error one might face post-conversion:

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In this example, the error is due to the use of as, which is a TypeScript-only construct, and attempts to use provider as a value instead of a type.

The Solution

Step 1: Remove TypeScript-only Syntax

The first step in converting TypeScript to JSDoc is to eliminate TypeScript-specific syntax. The as keyword is not valid in plain JavaScript and should be removed.

Step 2: Utilize JSDoc Annotations

In place of TypeScript types, use JSDoc annotations to specify the types for your variables:

For the svelteKitAuthConfig, the JSDoc annotation would look like this:

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Similarly, for provider, annotate it as:

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Step 3: Reorganize Your Code

If you're using a type as a value (e.g., provider), it’s essential to extract it to a separate constant or directly use the JSDoc type without the as keyword.

Here's an example of how to restructure the code:

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Final Thoughts

Converting TypeScript to JSDoc involves careful elimination of TypeScript-specific syntax and the correct use of JSDoc annotations. Following these steps should help you avoid common pitfalls and streamline the process of converting your TypeScript code. Stick to these guidelines and you’ll find the conversion less daunting and far more manageable.

By harnessing the power of JSDoc, you can maintain clarity and type safety in your JavaScript projects, while leveraging existing TypeScript codebases effectively.