How do you add .json() to fetch Promises in JavaScript?

Use Object.defineProperties on the Promise to attach non-enumerable methods that .then() to Response.json(). See ffetch's attachResponseShortcuts.

Does decorating Promises break native fetch behavior?

No — await still yields plain Response. Props don't touch resolution, prototype, or standard ops.

Is ffetch's Promise decoration safe for production plugins?

Yes, with Symbol guards against duplicates. Locked props prevent overwrites, prioritizing stability.

What's the catch with non-configurable properties on Promises?

Can't mock or override easily — deliberate for safety in shared plugin ecosystems.

🛠️ Developer Tools

The JavaScript Hack That Slaps .json() Onto Fetch Promises Without Wrecking Native Behavior

Sick of fetch boilerplate? This ffetch trick lets you chain .get().json() directly, but without sacrificing the plain Response everyone expects. Smart—or just asking for bugs?

theAIcatchup Apr 10, 2026 4 min read

Code snippet showing Promise decorated with .json() method for ffetch fetch wrapper

⚡ Key Takeaways

Decorate Promises in-place with defineProperties for chainable Response methods like .json(). 𝕏
Non-enumerable, locked props prevent pollution and accidents while preserving native semantics. 𝕏
Symbol guard avoids double-decoration in plugin systems; thin .then() pass-throughs keep it lightweight. 𝕏

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#JavaScript Promises #Promises #api-ergonomics #fetch API #ffetch #javascript #javascript-fetch #native-semantics #promise-decoration

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Originally reported by Dev.to

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