Decorating Promises Without Breaking Them

The approach described in your blog post is an interesting and elegant way to enhance JavaScript objects, specifically Promise<fetch.Response> instances, by adding useful methods without altering their fundamental nature or breaking existing code that relies on them. Here are some key points and insights from the technique:

Key Points

1. Idempotency: The method ensures that decorating a promise is safe even if multiple plugins attempt to do so. This is achieved using a Symbol as an idempotence marker.

2. Type Safety: TypeScript types are used to ensure that the decorated promises still conform to their original type (Promise<fetch.Response>), but also include the new methods when the plugin is installed.

3. Non-Invasive: The technique does not alter the underlying Response object or its behavior, ensuring compatibility with existing code and libraries.

4. Opt-in Ergonomics: Users can benefit from convenience methods without changing their existing fetch patterns, making it a non-disruptive enhancement.

Implementation Details

Idempotency Marker

typescript
 
1const DECORATED = Symbol('ffetch.responseShortcutsDecorated');
2
3function attachResponseShortcuts(promise: Promise<Response>): Promise<Response> {
4  if ((
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6[Read the full article at DEV Community](https://dev.to/gkoos/decorating-promises-without-breaking-them-2jf4)
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